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)
Martinez
J R
JR
Department of Child Health, University of Missouri School of Medicine, Columbia 65212.
Cassity
N
N
Reed
P
P
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002712:Chlorides / Q000493:pharmacokinetics*; D005576:Colforsin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013363:Submandibular Gland / Q000187:drug effects / Q000378:metabolism*
D002712:Chlorides; D005576:Colforsin; D003994:Bucladesine; D007545:Isoproterenol