β-Adrenergic-induced Calcium Efflux in Rat Parotid Gland. Is Mitochondrial Na⁺/Ca²⁺ Exchange Involved?

Abstract

The effects of diltiazem were examined on ⁴⁵Ca efflux in rat parotid glands. First, we showed that mitochondrial Na⁺/Ca²⁺ exchange occurs in rat parotid glands and that diltiazem inhibited the mitochondrial Na⁺-dependent calcium efflux. We also confirmed that in rat parotid gland, diltiazem did not modify calcium movements at plasma membrane level. Secondly, we tested the effects of diltiazem on pieces of parotid glands. Diltiazem alone induced ⁴⁵Ca efflux from parotid lobules. When the effect of diltiazem was tested on isoproterenol-induced ⁴⁵Ca efflux, the effects of the two drugs were less than additive. By comparison, diltiazem did not modify carbachol induced ⁴⁵Ca efflux. Diltiazem was able to induce calcium efflux from an intracellular calcium pool, which is not the IP₃ sensitive one. These data support the previous hypothesis that isoproterenol and carbachol do not mobilize the same calcium pool. Although we did not precisely determine the calcium pool sensitive to β-adrenergic stimulation, we cannot rule out the hypothesis that mitochondria would be that store.