Stimulation of Rb+ transport by glucagon in isolated rat hepatocytes.

Glucagon caused a 2-2.5-fold increase in 86Rb+ (a K+ tracer) uptake in primary monolayers of rat hepatocytes. Removal of the hormone led to a slow reversal of the effect over a period of hours. Glucagon acted by increasing the maximum velocity of influx. Ouabain inhibited Rb+ uptake in both hormone-induced and control cells by 85-90%. Hormone stimulation and ouabain inhibition did not affect exit. The induction by glucagon required 3-4 h for full expression and was dependent on protein synthesis and changes in cAMP. Half-maximum stimulation occurred at a concentration of 0.4 nM of the hormone. The ionophores monensin and gramicidin, which lead to Na+ influx, stimulated ouabain-sensitive Rb+ transport. This suggested that the (Na,K)-pump rate is limited by the internal Na+ concentration in both glucagon-stimulated and control cells.