Ionic dependence of electrical activity in small mesenteric arteries of guinea-pigs

The regulation of blood vessel diameter is under the control of the autonomic nervous system (as well as hormones and metabolites), sympathetic nerve stimulation evoking depolarizing post-synaptic potentials. Excitatory junction potentials (EJPs) were recorded from vascular smooth muscle cells of guinea-pig small mesenteric arteries (pressurized) following nerve stimulation. Repetitive stimulation (>5Hz) led to summation of EJPs, which evoked spikes and vasoconstriction. Replacing extracellular Na⁺ with choline (plus atropine) resulted in a decrease in EJP amplitude, but spike amplitude and maximum rate of rise (+V_max) were unaffected. Decreasing the extracellular Ca²⁺ concentration produced decreases in EJP amplitude and spike +V_max, while increasing extracellular Ca²⁺ resulted in increased EJP amplitude and spike +V_max. Verapamil and bepridil, agents that depress Ca²⁺ influx in vascular and visceral smooth muscle, depolarized the membrane and depressed EJPs and spikes at high concentrations (10^–5 M and 5×10^–6 M, respectively). The data indicate that EJPs are dependent on external Na⁺ and Ca²⁺ ions, and that spikes are dependent on Ca²⁺. Thus, neuromuscular transmission in this muscle is similar to that in non-vascular smooth muscles, such as intestinal muscle and vas deferens.Part of this work has been presented to the Biophysical Society (Zelcer and Sperelakis 1980) and to the American Physiological Society (Zelcer and Sperelakis 1981)