Modulation of cholinergic proteins and RNA by ouabain in chick muscle cultures

Extracellular potassium and the regulation of acetylcholine receptor synthesis in embryonic chick muscle cells

The effect of elevated extracellular potassium on acetylcholine receptor synthesis was studied in chick embryonic muscle cultures. At physiological ionic strength, potassium chloride, in the 3.3 to 50 mM range, gave rise to a complex dose-response curve whose prominent features are a considerable reduction of receptor appearance rate at 20 mM and a more than 2-fold increase at higher concentrations. The effect of potassium chloride on receptor synthesis appears to be fairly specific: neither was there a duplication of its effect by other electrolytes or solutes, nor did it alter total protein synthesis or receptor stability by more than 30% at any concentration tested; cellular acetylcholinesterase levels actually declined with increasing KCl concentrations. In order to explore the mechanism of the potassium effect, tetrodotoxin (10(-6) M), veratridine (3 X 10(-6) M), D-600 (1.6 X 10(-5) M), and ryanodine (3 X 10(-7) M) were tested in the presence of various concentrations of potassium. Sodium channel toxins as well as calcium effectors modified the potassium response. Based on these findings we propose that the effects of potassium are due to: (a) cessation of spontaneous muscle activity upon raising KCl from 3 to 10 mM; (b) depolarization of the muscle membrane and persistent activation of a calcium channel as concentration is raised from 10 to 20 mM; (c) finally, inactivation or desensitization of the calcium channel, or some other signaling element proximal to the sarcoplasmic reticulum, upon further depolarization.