Increase in membrane resistance during noradrenaline-induced depolarization in arterial smooth muscle

The effects of noradrenaline on membrane resistance of smooth muscle cells of the guinea-pig main pulmonary artery were assessed from the change in amplitude of electronic potentials produced by extracellularly applied current pulses. Noradrenaline was applied exogenously by bath application or endogenously by stimulating perivascular nerves. Exogenous noradrenaline depolarized the smooth muscle membrane with an associated increase in amplitude of electrotonic potentials and produced spike responses. Perivascular nerve stimulation evoked an excitatory junction potential with slow time course. The amplitude of electrotonic potential was slightly decreased during generation of the excitatory junction potential, but the reduction was less than that observed during current-induced depolarization. These observations suggest that the depolarizations produced by either endogenous or exogenous noradrenaline are accompanied by an increase in membrane resistance of arterial smooth muscle.