The calcium requirement for stimulation of rubidium efflux from isolated rat parotid acinar cells by carbachol.

Stimulation of ⁸⁶Rb⁺ efflux from isolated parotid acinar cells by carbchol was biphasic. The phases of stimulated ⁸⁶Rb⁺ efflux were separated on the basis of their relative requirements for extracellular Ca²⁺. If the isolated cells were incubated in Ca²⁺ free buffer containing 1.0 mM ethylene glycol bis (β-aminoethyl ether) N, N¹ - tetra acetic acid (EGTA) for 30 min. before adding carbachol an initial phase of ⁸⁶Rb⁺ efflux was observed. A second phase of ⁸⁶Rb⁺ efflux was obtained upon addition of 2.0 mM Ca²⁺. However when cells were incubated for 60 min. in Ca²⁺ free buffer containing 1.0 mM EGTA the initial phase of release caused by carbachol was inhibited by 95 percent. If the EGTA was titrated with Ca²⁺ to give 1.0 mM Ca²⁺, following the 60 min. depletion regimen, the second phase was observed. Although 60 min. of Ca²⁺-depletion in EGTA buffer was required for complete inhibition of the effect of carbachol on the initial phase of ⁸⁶Rb⁺ efflux, the response was fully restored within 4 min. after the readdition of Ca²⁺.