CA2- INTERPLAY BETWEEN CA2+ RELEASE FROM INTRACELLULAR STORES AND MEMBRANE-POTENTIAL( SIGNALING IN RAT CHROMAFFIN CELLS )

Cytosolic Ca2+ oscillations are physiologically important in a range o f excitable and non-excitable cells. The combined techniques of whole- cell patch clamp and photometric measurement of cytosolic Ca2+ has ena bled us to identify the components of Ca2+ spiking in rat chromaffin c ells. We show that Ca2+ oscillations continue at a fixed membrane pote ntial and that infusion of the InsP(3) receptor antagonist, heparin, s ubstantially blocked the cytosolic Ca2+ spikes. However, even in the p resence of heparin we observed spikes of membrane potential depolariza tion due to the repetitive activation of a transient inward cation cur rent. We conclude that Ca2+ oscillations are dependent on Ca2+ release from heparin sensitive Ca2+ stores and possibly on Ca2+ entry associa ted with the repetitive activation of a transient cation current. The depolarizing action of the cation current would, in turn, recruit volt age-sensitive Ca2+ channels and further Ca2+ entry would augment the c ytosolic Ca2+ spikes. Our results demonstrate that Ca2+ oscillations i n rat chromaffin cells are due to a complex interplay of Ca2+ entry an d Ca2+ release.