Effects of isoproterenol on Cl transport in rat submandibular salivary-gland acini.

In the absence of the beta-adrenoceptor agonist, isoproterenol, acini accumulated 36Cl in a time-dependent manner until a steady-state content of 7.4 +/- 0.2 nmol/mg protein was attained after 5 min of incubation. In the presence of 10 microM isoproterenol the tracer content increased significantly in the first few minutes (40 per cent after 2 min, 33 per cent after 5 min) but then decreased and was essentially the same as in the absence of agonist after 15 min. This effect was inhibited by 1 mM furosemide but was still observed when the cells were incubated in K-free medium. Exposure of tracer-preloaded cells with steady-state isotope content to 10 microM isoproterenol likewise caused a transient but significant increase in tracer content (32 per cent after 6 min); exposure to 1 microM acetylcholine caused a significant and sustained decrease in tracer content (30 per cent), which was not prevented by pre-incubating the cells for 5 min with isoproterenol. Similar transient increases in tracer content of preloaded cells were observed upon exposure to 10 microM concentrations of forskolin or dibutyryl cAMP. Stimulation of beta-receptors does not therefore cause a net Cl efflux in salivary acini and does not prevent the net efflux induced by stimulation of cholinergic receptors. As this efflux may be via a conductance pathway or channels in the apical membrane, these channels do not seem to be regulated by a beta-receptor-coupled, cAMP-mediated pathway in salivary cells.(ABSTRACT TRUNCATED AT 250 WORDS)