SPIKE GENERATING SMOOTH-MUSCLE CELLS IN MESENTERIC-ARTERY OF RATS

Membrane electrical properties of smooth muscle cells at different loc i in the vessel wall of rat small mesenteric arteries were studied usi ng glass microelectrodes. Isometric force was measured simultaneously. Penetrations of smooth muscle cells on the adventitial side (outer ce lls) showed an average resting potential, -43.1+/-0.8 mV (n=24). In ou ter cells, numerous depolarizing junctional potentials and, to a lesse r degree, hyperpolarizing junctional potentials were observed. When cu rrent was injected, electrotonic potentials were recorded. Input resis tance was 2.2+/-0.1x10(9) Omega (n=15), suggesting that the low resist ance pathways commonly observed in smooth muscle tissue are absent amo ng these cells. Transmural electrical stimulation of nerves elicited s pikes and summation of junctional potentials, accompanied by force. TT X virtually abolished these effects of the transmural stimulation. In contrast, cells near the intima (inner cells) had an average resting p otential 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 arte ries differ from the inner cells in their lower membrane potentials, g eneration 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.