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

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Abstract
The effect of the .beta.-adrenergic agent isoproterenol (ISO) on 42K influx into isolated smooth muscle cells of the toad [Bufo marinus] was investigated. Unidirectional 42K influx studies were carried out as described previously using suspensions of smooth muscle cells derived from the toad stomach. ISO (10-4 M) produces an approximate 3-fold 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 .times. 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 cAMP. The hypothesis that ISO elicits a .beta.-adenergic, cAMP-dependent activation of the Na+-K+ pump in isolated smooth muscle cells is evidently supported.