Ca2 + Dynamics in chemoreceptor cells: an overview

21 Ca2+ DYNAMICS IN CHEMORECEPTOR CELLS: AN OVERVIEW C. González,J.R. López-López,A. Obeso,A. Rachee and J. Ga cía -Sancho Op o. Bioquímica y Biología Molecula y Fisiología, Facul ad de Medicina, Uni e sidad de Valladolid, 47005 Valladolid, Spain The ca o id body (CB) was de ined as a senso y o gan by De Cas o in 1928. Two yea s la e , Heymanns and cowo ke s demos a ed ha he o gan was sensi i e o al e a ions in blood gases and pH, in such a way ha a dec ease in blood P02 o pH o an inc ease in blood PC02 p oduced ac i a ion o he CB and, e lexely, hype en ila ion. De Cas o pos ula ed ha glomus cells we e he senso s uc u es and ha hey should elease so ne subs ance o ansmi he s imulus o he senso y ne e endings (De Cas o, 1928). De Cas o's poin o iew, was widely accep ed, and he e o e he CB was conside ed a seconda y senso y ecep o . As a consequence, he p incipal aims o man y wo ke s in he chemo ecep ion ield ha e been o de ine he na u e o he sensing mechanims ( senso y ansduc ion p ocess ) and o iden i y he subs ances eleased by che no ecep o cells. The ini ial expe imen al app oaches o hese ques ions we e based on he use o "in i o" p epa a ions. The physiological ole o CB in sys emic e lexes was es ablished and he "in i o" p epa a ion led also o so ne hypo hesis abou he senso y ansduc ion p ocess. The me abolic and he acidic hypo hesis we e de eloped (Fidone and Gonzalez 1986). Howe e , he uly in ima e unc ional aspec s o he chemo ecep ion p ocess emained unde ined. I became necessa y o look o al e na i e expe imen al app oaches, and an elegan "in i o" p epa a ion was de eloped by Eyzagui e and Lewin in 1961. Howe e Eyzagui e's p epa a ion was no well accep ed; he esul s ob ained in "in i o" p epa a ions we e c i icized, a guing ha he CB was no unc ional o ha i was dead (see diseussion in To ance, pp. 248 and 298 and in Acke e al., 1977 pp. 76-77). Gene al accep ance o he p epa a ion had o awai un il he se en ies, when Whalen and Nai (1976) and S a linge and Lübbe s (1976) demos a ed ha he CB "in i o" exhibi ed P02 le els and 02 consump ion a es e y simila hose ound "in i o". Ul as . nc u al analysis o he CB a e "in i o" supe usion showedexcellen p ese a ion o he issue (Ve na e al., 1981). The "in i o" p epa a ion o e ed a well con olled sys em o s udy basic mechanisms, including neu o ansmi e syn hesis and elease. In he la e six ies, a conside able backg ound exis ed in he ield o neu o ansmission and sec e ion in gene al. Ka z and Miledi ( 1965) had demos a ed he ole o Ca2+ in he elease o ace ylcholine in he neu omuscula junc ion. S udies pe o1med in he ad enal medulla led o simila esul s and o he p oposal o he concep o s imulus-sec e ion coupling by Douglas in 1968. In his scheme, ace ylcholine would p oduce an inc ease in memb ane pe meabili y, an in lux o Ca2+ and he sec e ion o ca echolamines. Douglas iewed s imulus-sec e ion eoupling as a gene al concep , ha should be common o man y di e en cells; he di e ences would be he na u e o he s imulus and o he eleased subs ances. Sec e ion s udies caiTied ou in o he p epa a ions as neu ohypophysis Neu obiology and Ce/1 Physiology o Chenw ecep ion Edi ed by P.G. Da a e al., Plenum P ess, New Yo k, 1993 149