36Cl fluxes in dispersed rat submandibular acini: effects of acetylcholine and transport inhibitors.

Acini isolated from the rat submandibular gland showed uptake of 36Cl in the absence of added test substances. A steady state of 36Cl content corresponding to 9.5 +/- 0.7 nM/mg protein was attained in 4-5 min and maintained for 25-30 min. This uptake of 36Cl was reduced 40-50% by previous exposure to 10(-3) M furosemide, 10(-3) M ouabain, or K+-free medium. The steady state of 36Cl content was reduced 34% by 10(-6) M acetylcholine while exposure of the acini to the stilbene sulfonic DIDS (10(-3) M) did not modify 36Cl uptake either in the absence (basal) or presence of acetylcholine. Acetylcholine caused a rapid reduction of 36Cl from tracer-preloaded acini (42% in 1 min), while furosemide induced a slower reduction of tracer content (45% in 9 min). Acetylcholine increased the rate of reduction of tracer content induced by furosemide and the latter caused a further reduction in 36Cl content of acini previously exposed to acetylcholine. It is concluded that a furosemide-sensitive Cl uptake is present in rat submandibular acini, which depends on the Na+ gradient generated by the Na, K pump and on external K+. These findings suggest that a Na-K-Cl cotransport system driven by the Na, K pump is present in salivary acinar cells. Acetylcholine induces a rapid net efflux of 36Cl, which probably masks any effect that this secretagogue may have on Cl uptake. The lack of effect of DIDS on 36Cl uptake suggests that anion exchange transport systems are either not present in rat submandibular acini or can only be ascertained under different incubation conditions.