Mechanism of electrical stimulation-induced subsensitivity of vascular smooth muscle

Direct electrical stimulation (DES) of the smooth muscle in the wall of rabbit ear artery results in decreased responsiveness to subsequent exposure to norepinephrine, histamine and serotonin, but not potassium. DES had no effect on the transient contraction in ear arteries, to histamine that had been exposed to calcium-free Krebs' solution for 5 min. Calcium added in the continued presence of histamine elicited decreased tonic contractions in directly stimulated tissues. Directly stimulated everted vessels removed from surgically denervated or normal rabbits responded to norepinephrine or histamine with initial transient contractions identical to that of their respective rested everted controls. In contrast, however, the second phase tonic responses were depressed. The subsensitivity was almost completely prevented by DES in the presence of KCI or papaverine. When histamine, norepinephrine or sympathetic nerve stimulation were applied concomitantly with the DES, similar levels of subsensitivity were found. It is hypothesized that prior electrical stimulation may decrease responsiveness by reducing the effectiveness of coupling between the agonist-receptor activation of increased calcium permeability.