POTASSIUM RELEASE FROM RAT SUBMAXILLARY-GLAND INVITRO .1. INDUCTION BY CATECHOLAMINES

Abstract

Slices of submaxillary gland were incubated in vitro in an enriched Krebs-Ringer-bicarbonate medium gassed with 95% O2-5% CO2 at 37.degree. C, and the release of K+ into the medium was monitored after stimulation with .alpha. and .beta. adrenergic secretagogues under a variety of experimental conditions. K+ was released by the slice system after addition of norepinephrine, epinephrine or phenylephrine, but not after addition of isoproterenol. The extent of K+ release after norepinephrine depends on the dose of secretagogue and is higher when glucose, adenine and inosine or all 3 substrates are absent from the medium. The effect of norepinephrine on K+ release is reversed by phentolamine but not by propranolol. Phentolamine also causes a 9.4-fold shift to the right in the dose-response curve to norepinephrine. Addition of ouabain to the incubation medium results in a higher extent of K+ release and prevents the reversal caused by phentolamine. The response to norepinephrine fails to occur when Ca2+ is absent from the medium, either by chelation with ethylene glycol bis(.beta.-aminoethyl ether)-N,N''-tetraacetic acid or by elimination from the Krebs-Ringer solution, and shows gradations depending on the Ca2+ content of the medium. By itself, however, Ca2+ does not induce K+ release from the slice system. The release of K+ from the submaxillary gland is mediated by .alpha. adrenergic receptors. The net amount of K+ released is the result of 2 opposing and almost simultaneous mechanisms, a passive extrusion and an active reuptake. The active reuptake of K+ depends on the availability of energy and is mediated through the ouabain-sensitive Na+-K+ activated ATPase. The reaction is critically dependent on the presence of Ca2+ in the incubation medium and probably involves an influx of Ca2+ upon stimulation with .alpha. adrenergic secretagogues.