Beta-adrenergic stimulation of 42K influx in isolated smooth muscle cells.

Abstract

The present studies were designed to examine the effect of the beta-adrenergic agent isoproterenol (ISO) on 42K influx into isolated smooth muscle cells. Unidirectional 42K influx studies were carried out as described previously using suspensions of smooth muscle cells derived from the toad stomach. Results from these studies indicated that ISO (10(-4) M) produces an approximate threefold increase in 42K influx within 1 min after drug addition. This response is transient such that the flux rate returns to near basal levels within 5 min after drug addition. The stimulatory effect of ISO on 42K influx is blocked by pretreatment with ouabain (1-7.5 X 10(-4) M). ISO thus appears to increase 42K influx by stimulating the Na+-K+ pump in the smooth muscle cells. Other findings indicate that the stimulatory effect of ISO on Na+-K+ pumping is dose dependent, blocked by the beta-antagonist pindolol, and mimicked by dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP). These findings support our hypothesis that ISO elicits a beta-adrenergic, cAMP-dependent activation of the Na+-K+ pump in isolated smooth muscle cells.