Spike generating smooth muscle cells in mesenteric artery of rats

Membrane electrical properties of smooth muscle cells at different loci in the vessel wall of rat small mesenteric arteries were studied using glass microelectrodes. Isometric force was measured simultaneously. Penetrations of smooth muscle cells on the adventitial side (outer cells) showed an average resting potential, -43.1 +/- 0.8 mV (n = 24). In outer cells, numerous depolarizing junctional potentials and, to a lesser degree, hyperpolarizing junctional potentials were observed. When current was injected, electrotonic potentials were recorded. Input resistance was 2.2 +/- 0.1 x 10(9) omega (n = 15), suggesting that the low resistance pathways commonly observed in smooth muscle tissue are absent among these cells. Transmural electrical stimulation of nerves elicited spikes and summation of junctional potentials, accompanied by force. TTX virtually abolished these effects of the transmural stimulation. In contrast, cells near the intima (inner cells) had an average resting potential of -65.8 +/- 0.9 mV (n = 37). No spontaneous electrical activity was observed; nor could electrotonic potentials be recorded. Thus, the smooth muscle cells from the outer layer of rat small resistance arteries differ from the inner cells in their lower membrane potentials, generation of spikes, higher input resistance and innervation. Results also suggest that the influence of nerves may be to facilitate opening of voltage-gated Ca2+ channels in innervated cells.