36Cl fluxes in dispersed rat submandibular acini: effects of Ca2+ omission and of the ionophore A23187.

Transmembrane fluxes of 36Cl were investigated in dispersed acini of the rat submandibular gland in Ca2+-containing and Ca2+-free media and also in the presence of the divalent cation ionophore A23187. In Ca2+-replete medium, a time-dependent uptake of tracer resulted in a steady state 36Cl content of 8.5 +/- 0.3 nmol/mg protein in 3-5 min. This uptake was reduced 32% by 1 mM furosemide and 27% by 1 microM acetylcholine. In the presence of Ca2+, the ionophore (10(-5) M) reduced tracer uptake 36% and prevented further effects of either acetylcholine or furosemide. Both acetylcholine and A23187 caused a rapid net efflux of 36Cl from tracer-preloaded acini in Ca2+-containing medium (37% and 20%, respectively). When Ca2+ was omitted from the incubation medium, basal 36Cl uptake in the absence of added test substance was the same as in Ca2+-containing medium but was not affected by acetylcholine, while it was still reduced 29% by furosemide. Addition of acetylcholine to preloaded acini in Ca2+-free medium caused only a transient and unsustained 36Cl efflux but subsequent addition of Ca2+ produced a 36% reduction in tracer content. The ionophore caused a net 36Cl efflux in Ca2+-containing medium (24% decrease in 36Cl content) but had no effect in Ca2+-free medium. Subsequent addition of Ca2+ resulted in a 27% net efflux of tracer. The calmodulin inhibitor trifluoperazine caused a 14% increase in 36Cl uptake but did not cause 36Cl efflux from preloaded cells or modify acetylcholine-induced efflux of tracer from these cells.(ABSTRACT TRUNCATED AT 250 WORDS)