Hormonal Regulation of chicken intestinal NHE and SGLT-1 activities

Ho monal egula ion o chicken in es inal NHE and SGLT-1 ac i i ies MARIA CARMEN DE LA HORRA, MERCEDES CANO, MARIA JOSE ´PERAL, MARIA LUISA CALONGE, AND ANUNCIACIO ´N ANA ILUNDA ´IN Depa amen o Fisiologı´a y Biologı´a Animal, Facul ad de Fa macia, Uni e sidad de Se illa, 41012 Se illa, Spain Recei ed 27 Ma ch 2000; accep ed in inal o m 23 Oc obe 2000 De La Ho a, Ma ia Ca men, Me cedes Cano, Ma ia Jose´ Pe al, Ma ia Luisa Calonge, and Anunciacio´n Ana Ilunda´in. Ho monal egula ion o chicken in es inal NHE and SGLT-1 ac i i ies. Am J Physiol Regula o y In e- g a i e Comp Physiol 280: R655–R660, 2001.—The e ec s o aldos e one and a ginine aso ocin (AVT) on in es inal Na ⫹ /H ⫹ exchange (NHE) and Na ⫹ -suga co anspo (SGLT-1) ac i i- ies ha e been in es iga ed using b ush-bo de memb ane es- icles isola ed om Hubba d chicken small and la ge in es ines, and hey we e compa ed wi h hose induced by ei he Na ⫹ deple ion o dehyd a ion. Na ⫹ deple ion was induced by eeding he chickens wi h ei he a low- o a high-Na ⫹ die o ei he 0.5, 1, 2, 4, o 8 days. Ileal and colonic NHE2 ac i i y inc eased wi h he du a ion o he Na ⫹ deple ion, whe eas ha o in es inal SGLT-1 dec eased, eaching a pla eau a e 2 days o ea - men . Th ee-hou incuba ion o he in es ine wi h aldos e one p oduced he same e ec s on NHE ac i i y as does Na ⫹ deple- ion, wi hou al e ing SGLT-1 ac i i y. Howe e , 3-h incuba ion o he in es ine wi h AVT inc eased in es inal SGLT-1 ac i i y, wi hou a ec ing in es inal NHE ac i i y. I is concluded ha aldos e one egula es apical ileal and colonic NHE2 ac i i y, whe eas ha o SGLT-1 is egula ed by AVT. low-Na ⫹ die ; aldos e one; a ginine aso ocin; b ush-bo de memb ane esicle; sodium/hyd ogen exchange IN MAMMALS,THE KIDNEY and he la ge in es ine a e he majo egula o s o body elec oly e and wa e ho- meos asis. As bi ds do no ha e a u ina y bladde , he u ine is emp ied in o he cloaca, and e og ade low ca ies u ine in o he cop odeum, he colon ( ec um), and cecum. As a esul , he epi helia o he lowe in es ine p ocess he ileal and u e e al ou low. We p e iously epo ed ha die a y Na ⫹ deple ion de- c eased Na ⫹ -suga co anspo (SGLT-1) ac i i y and inc eased ha o apical sodium/hyd ogen exchange (NHE) in he chick ileum and colon (6, 7). We also showed (6) ha 4 days o wa e dep i a ion inc eased he ac i i ies o bo h apical NHE and SGLT-1 in jeju- num, ileum, and colon o he chicken. The e o e, Na ⫹ deple ion dec eased in es inal SGLT-1 ac i i y, whe eas i was inc eased by dehyd a ion. Because bo h ea men s inc eased plasma aldos e one le els, i was concluded ha aldos e one does no egula e in es inal SGLT-1 (6). The pu pose o he cu en wo k was o in es iga e in b ush-bo de memb ane esicles (BBMV) isola ed om chicken small and la ge in es ine he ime cou se o he e ec s o Na ⫹ deple ion on in es inal NHE and SGLT-1 ac i i ies and he e ec s o aldos e one and a ginine aso ocin (AVT) on hose Na ⫹ -linked ans- po sys ems ac i i ies. MATERIALS AND METHODS Solu ions. Fo 22 Na ⫹ up ake expe imen s, he in a esicu- la bu e con ained (in mM) 140 manni ol, 50 K-glucona e, and 50 Mes-T is (pH 5.5). The up ake bu e consis ed o (in mM) 140 manni ol, 50 K-glucona e, 0.045 alinomycin, 0.1 Na-glucona e, ace s o 22 Na ⫹ , and ei he 50 Mes-T is (pH 5.5) o 50 HEPES-T is (pH 7.5). The s op solu ion con ained (in mM) 140 manni ol, 50 K-glucona e, 50 Mes-T is (pH 5.5), and 0.1 amilo ide. The p o ein concen a ion pe assay ube was 100–150 ␮g/100 ␮l o up ake bu e . ␣-Me hyl-glucopy anoside (␣-MG) up ake was measu ed in BBMV loaded wi h (in mM) 140 manni ol, 50 K-glucona e, 0.1 MgSO 4 , and 50 HEPES-T is (pH 7.5). The ex a esicula bu e con ained (in mM) 140 manni ol, 50 Na-glucona e, 0.1 ␣-MG, 0.045 alinomycin, and ace s o ␣-[D- 14 C]MG and 50 HEPES-T is (pH 7.5), wi h o wi hou 0.25 phlo izin. The s op solu ion con ained (in mM) 140 manni ol, 50 HEPES- T is (pH 7.5), 50 K-glucona e, and 0.25 phlo izin. The p o ein concen a ion pe assay ube was 100 ␮g/100 ␮l o up ake bu e . The e e ed small and la ge in es ines we e incuba ed o 3 h in a solu ion con aining (in mM) 90 manni ol, 80 NaCl, 1 CaCl 2 , 1 MgCl 2 ,3K 2 HPO 4 ,25HCO 3 choline (pH 7.4), and he desi ed ho mone, and i was con inuously bubbled wi h 95% O 2 and 5% CO 2 . The medium was also supplemen ed wi h 10 mM glucose, 100 U/ml penicillin, and 100 ␮g/ml s ep omycin. The pH o he solu ion was con olled h ough- ou he expe imen . Animals and die s. Two g oups o Hubba d chickens, 10 wk old, we e adap ed, be o e being killed, o ei he 0.5, 1, 2, 4, o 8 days o ei he a high-NaCl die o a low-NaCl die as desc ibed (14). The low-NaCl ea men consis ed o low- NaCl balanced ood and demine alized wa e con aining 1 mM CaCl 2 . The high-NaCl ea men consis ed o high-NaCl Add ess o ep in eques s and o he co espondence: A. A. Ilunda´in, Dep . Fisiologı´a y Biologı´a Animal, Facul ad de Fa macia, C) T amon ana s/n, 41012 Se illa, Spain (E mail: [email p o ec ed]). The cos s o publica ion o his a icle we e de ayed in pa by he paymen o page cha ges. The a icle mus he e o e be he eby ma ked ‘‘ad e isemen ’’ in acco dance wi h 18 U.S.C. Sec ion 1734 solely o indica e his ac . Am J Physiol Regula o y In eg a i e Comp Physiol 280: R655–R660, 2001. 0363-6119/01 $5.00 Copy igh ©2001 he Ame ican Physiological Socie yh p://www.ajp egu.o g R655 balanced ood and demine alized wa e con aining 1 mM CaCl 2 plus 0.5% NaCl (w / ol). Ano he g oup o chickens was ed a comme cial die o 10 wk. A e chickens we e killed wi h an in a enous injec ion o u e hane, he small and la ge in es ines we e emo ed, opened longi udinally, insed clean wi h ice-cold saline solu- ion, and incuba ed o 3hin heabsence o p esence o ei he 0.5 ␮M aldos e one o 0.5 ␮M AVT. Plasma analysis. Blood samples we e collec ed om a wing ein in o ice-cold hepa inized ubes and cen i uged immedi- a ely a 4°C. Plasma aldos e one was measu ed by adioim- munoassay by Ce ba labo a o ies (Ba celona, Spain). Na ⫹ and K ⫹ we e measu ed by lame pho ome y and osmolali y wi h an osmome e (Osmome e Gono ec, Osmoma 030). Glucose was measu ed enzyma ically. Glucose, Na ⫹ ,K ⫹ , and osmolali y o he in es inal con en . The animals we e killed by in a enous injec ion o u e- hane, he issues we e emo ed, and he con en o jejunum, ileum, o colon was emp ied in o cen i uge ubes. A e cen i uga ion a 5,000 pm a 4°C o 20 min, samples we e aken om he supe na an and es ed o Na ⫹ ,K ⫹ , glucose, and osmolali y as desc ibed abo e. BBMV p epa a ion. The small and la ge in es ines we e insed wi h ice-cold saline solu ion and opened longi udi- nally. The mucose was sc aped o wi h a glass slide, w apped in aluminum oil, ozen in liquid ni ogen, and kep a ⫺80°C un il use. BBMV we e isola ed om ei he jejunum o ileum as desc ibed by Pe al e al. (12). B ie ly, he mucose was hawed in a bu e con aining (in mM) 100 manni ol, 2 HEPES-T is (pH 7.1), 0.2 phenylme hylsul onyl- luo ide (PMSF), 0.5 DL- di hio h ei ol, and 0.2 benzamidine, homogenized in a Wa - ing blende (model 32 BL80) a high speed o 30 s and il e ed h ough a Buchne unnel. MgCl 2 was added o he homogena e o a inal concen a ion o 10 mM. The suspen- sion was s i ed o 20 min and hen cen i uged a 3,000 g o 15 min. The plasma memb anes e ained in he supe na- an we e collec ed by cen i uga ion a 30,000 g o 30 min. The esul an pelle was suspended in a pH 7.4 bu e con- sis ing o (in mM) 100 manni ol, 2 HEPES-T is, and 0.1 MgSO 4 . This suspension was homogenized wi h 50 up-down s okes wi h a glass-Te lon homogenize , b ough up o 35– 40 ml wi h he same bu e , and cen i uged a 30,000 g o 30 min. The inal pelle , con aining he pu i ied BBMV, was suspended in he loading bu e s as desc ibed abo e. The inal suspension was homogenized by passing he suspension h ough 25- and 28-gauge needles. All he s eps we e ca ied ou a 4°C. BBMV we e isola ed om he colonic mucose, by he me hod desc ibed by Ha ig e al. (9), using Mg 2⫹ p ecipi a- ion ins ead o Ca 2⫹ p ecipi a ion as desc ibed in Calonge e al. (3). B ie ly, he mucose was de os ed in a solu ion (14 ml/g) con aining (in mM) 50 manni ol, 0.2 PMSF, 0.5 DL- di hio h ei ol, 0.2 benzamidine, and 2 HEPES-T is, pH 7.0; homogenized wi h a Ys al Poli on a se ing 4 o 90 s, and il e ed h ough a nylon gauze. MgCl 2 , a a inal concen a- ion o 10 mM, was added o he homogena e and s i ed o 20 min. The suspension was cen i uged a 1,000 g o 10 min, he esul an supe na an was cen i uged a 39,000 g o 20 min, and he esul an pelle was suspended in app o- p ia e loading bu e s. The suspension was homogenized wi h 20 up-down s okes wi h a glass-Te lon dounce homog- enize and cen i uged a 39,000 g o 30 min. The pelle was esuspended in he loading bu e s desc ibed abo e. The isola ed apical memb anes we e made homogenous by pass- ing hem h ough a 25- and a 26-gauge needle se e al imes; hey we e s o ed in liquid ni ogen un il use. All he s eps we e ca ied ou a 4°C. P o ein was measu ed by he me hod o Low y e al. (13) using albumin as he s anda d. Up ake s udies. 22 Na ⫹ o ␣-[D- 14 C]MG up ake was mea- su ed a 25°C by a apid il a ion echnique as desc ibed (4). B ie ly BBMV we e le o s and a oom empe a u e (⬃25°C) o 10 min. Timed incuba ions a oom empe a u e we e ini ia ed by adding 10 ␮l o suspended memb ane es- icles o 90 ␮l o up ake bu e (100–150 ␮g o p o ein/100 ␮l up ake bu e ). The composi ion o he up ake bu e s is gi en abo e. A e designa ed pe iods o ime, up ake was e mi- na ed by he addi ion o 2.5 ml o an ice-cold s op solu ion o he same composi ion as ha o he in a esicula bu e . The samples we e immedia ely il e ed unde acuum h ough a 0.45-␮m po e size Millipo e il e p ewe ed wi h he s op bu e . Fil e s we e u he washed wice wi h 5 ml o ice-cold s op solu ion, dissol ed in 5 ml o Ready-P o ein (Beckman) scin illa ion luid, and adioac i i y was de e - mined by liquid scin illa ion spec ome y. Nonspeci ic iso- ope binding o he il e s was de e mined sepa a ely by adding s op solu ion o he esicles be o e addi ion o up ake bu e and sub ac ed om he o al adioac i i y o each sample. All expe imen s we e done in iplica e. Ma e ials. 22 Na ⫹ o ␣-[D- 14 C]MG we e pu chased om Ame sham. Valinomycin, AVT, aldos e one, phlo izin, and all he sal s used in he cu en s udy we e ob ained om Sigma Chemical. HOE-694 was a gi om D . M. Donowi z. Calcula ions and s a is ics. Ve ical ba s in Figs. 1–5 ep- esen SE; hey a e absen when hey a e less han symbol heigh . Resul s a e exp essed as means ⫾SE. S a is ical signi icance was e alua ed by Dunne ’s es . RESULTS Adap a ion o a low-Na ⫹ die and plasma and in es- inal luid pa ame e s. Plasma aldos e one le els in- c eased nea ly hype bolically wi h he du a ion o he Na ⫹ deple ion om 13 o 170 pg/ml, wi h a hal - ime close o 1 day (Fig. 1). The plasma le els o ei he Fig. 1. Plasma aldos e one concen a ion plo ed s. he du a ion o Na ⫹ deple ion. Aldos e one was measu ed as explained in MATERIALS AND METHODS. Da a a e he mean alues ⫾SE o 4 animals. **P⬍ 0.01 compa ed wi h comme cial die (ze o ime). The da a a ime 15 days ha e been aken om a p e ious epo (7). R656 HORMONES AND ACTIVITY OF EITHER NHE OR SGLT-1 sodium o glucose o osmolali y we e no a ec ed by he ea men (Table 1). A e 12-h adap a ion o a low-Na ⫹ die , he K ⫹ concen a ion in he luminal luid o he h ee in es i- nal egions was inc eased (see Table 1). The ea men also inc eased glucose concen a ion in he in es inal con en , whe eas ha o Na ⫹ was dec eased un il al- ues we e unde ec able (see Table 1). In es inal luid osmolali y did no change in he small in es ine, and i was dec eased in he colon (see Table 1). Al hough he ood deli e y was nei he measu ed no con olled, i was no ed ha he animals ed on a low-Na ⫹ die ended o ea less ( he amoun o ood emaining in he con aine s was always g ea e han ha in hose con- aining high-Na ⫹ die ). Howe e , a dec ease in ood in ake would no explain he measu ed inc ease in bo h K ⫹ and glucose concen a ions in he in es inal con en ; hence hese obse a ions sugges ha in es i- nal anspo ac i i y was changed by he ea men . Na ⫹ con en in he die and Na ⫹ up ake in o BBMV isola ed om chick in es ine. Na ⫹ up ake in o chicken in es inal BBMV was measu ed in he p esence and absence o an inwa dly di ec ed pH g adien and unde memb ane ol age-clamped condi ions (equal in e nal and ex e nal po assium concen a ions plus alinomy- cin). The con ibu ion o ei he NHE2 o NHE3 o o al NHE ac i i y was de e mined using he amilo ide- ela ed d ug HOE-694 (50 ␮M), which in a and abbi has highe sensi i i y o NHE2 (K i ,5␮M) han o NHE3 (K i , 650 ␮M) (5, 16). The e o e, 50 ␮M HOE-694 will inhibi NHE2 ac i i y and will ha e no signi ican e ec on NHE3 ac i i y. The esul s e ealed (Fig. 2) ha jejunal NHE ac i - i y was no modi ied by Na ⫹ deple ion, whe eas bo h ileal and colonic NHE ac i i y inc eased wi h he ime o he du a ion o ea men , and he inc ease was due o inc eased NHE2 ac i i y. NHE3 ac i i y was no modi ied. Time-dependen e ec o Na ⫹ deple ion on SGLT-1 ac i i y in BBMV isola ed om chicken in es ine. Suga up ake in o in es inal BBMV was measu ed in he p esence o an inwa dly di ec ed elec ochemical Na ⫹ g adien , wi h o wi hou phlo izin. Feeding wi h a low-Na ⫹ die signi ican ly dec eased SGLT-1 ac i i y in jejunum, ileum, and colon (Fig. 3). The down egula ion o SGLT-1 ac i i y eached a pla- eau a 2 days o ea men . Low-Na ⫹ die did no a ec he phlo izin-insensi i e suga anspo compo- nen (da a no shown). E ec o ei he aldos e one o AVT on SGLT-1 and NHE ac i i ies in BBMV isola ed om he jejunum, ileum, and colon. BBMV we e isola ed om jejunum, ileum, and colon a e 3-h incuba ion wi h o wi hou 0.5 ␮M aldos e one o 0.5 ␮M AVT. Suga up ake and Na ⫹ up ake in o BBMV we e measu ed as indica ed abo e. The esul s show (Figs. 4 and 5) ha aldos e one and AVT a ec ed in es inal Na ⫹ -linked anspo sys ems ac i i y di e en ly. Thus aldos e one inc eased ileal and colonic NHE ac i i y, ia an inc ease in NHE2 ac i i y. Jejunal NHE ac i i y was no modi ied by aldos e one (da a no shown). On he o he hand, in- es inal NHE ac i i y was no signi ican ly modi ied by AVT. Table 1. Plasma and in es inal luid pa ame e s s. he du a ion o NaCl deple ion Days 0 0.5 1 2 4 8 Na ⫹ ,mM Jejunum 110⫾572⫾6† 56⫾8† 46⫾7† ⫺⫺ Ileum 108⫾575⫾4* 45⫾7† ⫺⫺⫺ Colon 93⫾6⫺⫺⫺⫺⫺ Plasma 137⫾4 130⫾3 128⫾2 148⫾2 135⫾3 137⫾2 K ⫹ ,mM Jejunum 16⫾122⫾129⫾2† 31⫾3† 26⫾2* 26⫾2* Ileum 14⫾122⫾135⫾3† 35⫾3† 38⫾4† 36⫾3† Colon 30⫾438⫾538⫾339⫾632⫾231⫾6 Plasma 6.3⫾0.1 9.4⫾0.7 8.2⫾0.3 8.4⫾0.3 8.7⫾0.4 9⫾0.5 Glucose, mM Jejunum 13⫾127⫾2† 41⫾0.2† 35⫾1† 41⫾1† 33⫾2† Ileum 7⫾0.4 14⫾1† 17⫾2† 14⫾1† 13⫾0.5† 15⫾1† Colon 1.2⫾0.1 5.2⫾0.6* NM 4.2⫾0.6 6.4⫾1† 7⫾1† Plasma 13⫾0.2 NM 12.8⫾0.3 13⫾0.3 13⫾0.8 14⫾1 Osmolali y, mosmol/KgH 2 O Jejunum 461⫾23 480⫾14 482⫾24 480⫾20 426⫾14 464⫾26 Ileum 407⫾22 389⫾17 400⫾14 418⫾8 378⫾28 394⫾2 Colon 300⫾15 230⫾12† 230⫾12† 220⫾12† 200⫾12† 200⫾12† Plasma 336⫾6 354⫾28 338⫾18 336⫾23 308⫾9 320⫾7 Values a e means ⫾SE (n⫽4 animals). Glucose, Na ⫹ and K ⫹ concen a ions, and osmolali y ha e been measu ed as desc ibed in MATERIALS AND METHODS. NM, nonmeasu ed. ⫺, unde ec able. *P⬍0.05, †P⬍0.001 as compa ed wi h high-Na ⫹ die (a day 0). R657HORMONES AND ACTIVITY OF EITHER NHE OR SGLT-1 Small and la ge in es inal SGLT-1 ac i i y was no modi ied by he in i o exposu e o he issues o aldos e one (Fig. 5), bu i was s imula ed by AVT. DISCUSSION The cu en esul s show o he i s ime ha AVT s imula es in es inal SGLT-1 ac i i y and co obo a e ou p e ious iew (6) ha aldos e one does no media e he e ec s o Na ⫹ deple ion on in es inal SGLT-1 ac- i i y. The ollowing obse a ions sugges ha aldos e one egula es ileal and colonic NHE2 ac i i y, bu i does no media e he dec ease in in es inal SGLT-1 ac i i y induced by Na ⫹ deple ion: 1) incuba ion o he in es- ine wi h aldos e one inc eased ileal and colonic NHE2 ac i i y as i does Na ⫹ deple ion; 2) SGLT-1 ac i i y was dec eased by Na ⫹ deple ion bu i was no a ec ed by aldos e one; and 3) he ime cou se o he e ec o Na ⫹ deple ion on plasma aldos e one le els is simila o ha on NHE2 ac i i y, bu no o ha on SGLT-1 ac i i y. We (6) ha e sugges ed ha , because Na ⫹ deple ion and dehyd a ion inc eased plasma aldos e one le els and p oduced opposi e e ec s on SGLT-1 ac i i y, al- Fig. 2. Adap a ion o a low-Na ⫹ die and sodium/hyd ogen exchange (NHE) ac i i y in b ush-bo de memb ane esicles (BBMV) isola ed om chicken in es ine. Na ⫹ up ake was measu ed in he p esence (5.5 i /7.5 o ) and absence (5.5 i /5.5 o ) o a p o on g adien , du ing 1 min o jejunum ( op) and ileum (middle) and 5 min in colon (bo om; ime o peak o e shoo alues). The composi ion o he in a- and ex a e- sicula bu e s a e gi en in MATERIALS AND METHODS. The concen a- ion o HOE-694 was 50 ␮M. When es ed, he esicles we e p ein- cuba ed wi h he inhibi o o 12 min. NHE ac i i y (1s F): Na ⫹ up ake measu ed in he p esence o a pH g adien minus ha measu ed in he absence o a pH g adien . NHE2 ac i i y (Œ): pH g adien -dependen Na ⫹ up ake sensi i e o HOE-694. NHE3 ac i - i y (2nd F): pH g adien -dependen Na ⫹ up ake insensi i e o HOE- 694. Da a a e mean alues ⫾SE o 4 sepa a e memb ane esicle p epa a ions. *P⬍0.05, **P⬍0.001, compa ed wi h high-Na ⫹ die (ze o ime). Fig. 3. Adap a ion o a low-Na ⫹ die and Na ⫹ -suga co anspo ac i i y in BBMV isola ed om chicken in es ine. ␣-Me hyl-glucopy- anoside (␣-MG) up ake in o BBMV was measu ed in he p esence o an inwa dly di ec ed elec ochemical Na ⫹ g adien , wi h o wi hou 0.25 mM phlo izin, o e 30 s o jejunum and ileum and 1 min o he colon ( ime o he peak o e shoo alues). Elec ical memb ane po en ial was c ea ed by an ou wa dly di ec ed K ⫹ g adien in he p esence o alinomycin. An inside di ec ed Na ⫹ g adien was c e- a ed by he addi ion o 50 mM Na ⫹ o he ex a esicula bu e . The in a esicula bu e was made nominally Na ⫹ ee. The da a ep e- sen he Na ⫹ -dependen , phlo izin-sensi i e suga up ake (SGLT-1 ac i i y), which is he o al suga up ake minus ha measu ed in he p esence o phlo izin. Da a a e mean alues ⫾SE o 4 sepa a e memb ane esicle p epa a ions. **P⬍0.001 compa ed wi h high- Na ⫹ die (ze o ime). R658 HORMONES AND ACTIVITY OF EITHER NHE OR SGLT-1 dos e one does no egula e in es inal SGLT-1. As plasma AVT le els a e inc eased by dehyd a ion (1) and dec eased by Na ⫹ deple ion (2), i was concluded (6) ha AVT could be he egula o o in es inal SGLT-1. The cu en esul s co obo a e his hypo he- sis, because he incuba ion o he in es ine wi h AVT inc eased small and la ge in es inal SGLT-1 ac i i y. In ou p e ious s udy (6) we also sugges ed ha AVT egula es jejunal NHE ac i i y because i was no a - ec ed by Na ⫹ deple ion, bu i was inc eased by dehy- d a ion. Howe e , he cu en esul s show ha nei- he aldos e one no AVT signi ican ly a ec ed jejunal NHE ac i i y. These esul s do no ag ee wi h p e ious epo s showing ha AVT inhibi s NHE3 ac i i y in Madin-Da by canine kidney cells ans ec ed wi h NHE3 (10). I could be concluded ha , in he chick, 1) apical NHE2 ac i i y in ileum and colon is egula ed by aldo- s e one and 2) small and la ge in es inal SGLT-1 ac- i i y is egula ed by AVT. The cu en esul s, how- e e , do no p o ide any clue o explain he inc ease in jejunal NHE ac i i y induced by dehyd a ion. I could be ano he ho monal ac o . The dec ease in in es inal SGLT-1 ac i i y induced by Na ⫹ deple ion could be due ei he o a dec ease in AVT sec e ion (2) o o he e ec o Na ⫹ con en in he in es inal lumen on he exp es- sion o he SGLT-1. Thus Na ⫹ deple ion educed Na ⫹ concen a ion in he in es inal con en un il alues we e unde ec able, and his dec ease was accompanied by an inc ease in glucose concen a ion in he in es i- nal con en . Fu he in es iga ion is equi ed o cha - ac e ize he molecula mechanisms unde lying he changes in ac i i y o he anspo e s unde s udy and o de e mine he link be ween Na ⫹ deple ion and in- es inal suga anspo ac i i y. A colla e al obse a ion o he cu en s udy is ha adap a ion o a low-Na ⫹ die inc eased he K ⫹ concen- a ion in he luminal luid o he h ee in es inal egions, indica ing ha he ea men s imula ed in- es inal po assium sec e ion, which ag ees wi h p e i- ous obse a ions in a colon (8, 15). Pe spec i es The cu en esul s ag ee wi h he idea ha he physiological ole o he la ge in es inal amilo ide- inhibi able Na ⫹ abso p ion is o conse e NaCl and ha o o ganic solu e-Na ⫹ co anspo is o conse e wa e (14) and sugges ha he small in es ine could also con ibu e o hese homeos a ic unc ions. Unde Na ⫹ deple ion, bo h he ex acellula luid olume and Fig. 5. E ec o ei he aldos e one (open ba s) o AVT (ha ched ba s) on SGLT-1 ac i i y in BBMV isola ed om chicken in es ine. The jejunum, ileum and colon we e incuba ed in he absence (con ol; solid ba s) and p esence o ei he 0.5 ␮M aldos e one o 0.5 ␮M AVT o 3 h, and BBMV we e p epa ed he ea e . O he de ails as in Fig. 3. Da a a e mean alues ⫾SE o 3 sepa a e memb ane esicle p epa a ions. **P⬍0.001 compa ed wi h issues no exposed o ho mones. Fig. 4. E ec o ei he aldos e one (open ba s) o a ginine aso ocin (AVT; ha ched ba s) on NHE ac i i y in BBMV isola ed om chicken in es ine. The ileum ( op) and colon (bo om) we e incuba ed in he absence (con ol; solid ba s) and p esence o ei he 0.5 ␮M aldos e- one o 0.5 ␮M AVT o 3 h, and BBMV we e p epa ed he ea e . O he de ails as in Fig. 2. Da a a e mean alues ⫾SE o 3 sepa a e memb ane esicle p epa a ions. *P⬍0.05, **P⬍0.001 compa ed wi h issues no exposed o ho mones. R659HORMONES AND ACTIVITY OF EITHER NHE OR SGLT-1 osmolali y all (11). Regula ion o ex acellula luid olume equi es Na ⫹ and wa e e en ion, and osmo- egula ion demands wa e exc e ion in a dilu ed u ine. The inc ease in Na ⫹ /H ⫹ exchange ac i i y and he dec ease in Na ⫹ -suga co anspo ac i i y, induced by he low-Na ⫹ die , will help o conse e Na ⫹ and o exc e e wa e , espec i ely. This will be achie ed by inc easing he plasma le els o aldos e one, which in- c eases Na ⫹ /H ⫹ exchange ac i i y, and by dec easing hose o AVT, which would educe SGLT-1 ac i i y. On he o he hand, he dehyd a ion-induced inc ease in bo h Na ⫹ /H ⫹ exchange ac i i y and Na ⫹ -dependen suga anspo will help o conse e bo h Na ⫹ and wa e , and, he e o e, o main ain bo h ex acellula luid olume and osmolali y wi hin accep able limi s. F om a physiological poin o iew, i is an ad an age ha he wo Na ⫹ -linked anspo sys ems a e egu- la ed by a di e en ho mone, which allows di e en egula ion o each anspo e acco ding o he homeo- s a ic demands o he o ganism. The po en ial physio- logical con ibu ion o la ge in es inal ac i e o ganic solu e co anspo could be ei he o p e en he loss o suga in he eces o o acili a e i acco ding o he homeos a ic needs o he animal. We hank F. F ie as o echnical help. 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