Electrical properties and morphology of single vascular smooth muscle cells in culture

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Abstract
Single vascular smooth muscle cells (VSMC) were isolated from the caudal artery and vein and studied after 2 or 3 days in culture. Current clamp with intracellular microelectrodes and "whole-cell" voltage-clamp techniques were used. Also, scanning and transmission electron microscopy studies were performed, revealing morphological characteristics of smooth muscle in culture. Cells could contract in response to electrical and chemical stimuli. The passive membrane properties recorded with intracellular microelectrodes in a mammalian saline were as follows: 1) for artery, resting potential Vm = -56 +/- 5 mV (mean +/- SD), input resistance Rin = 590 +/- 35 M omega, membrane time constant tau m = 19 +/- 2 ms, membrane capacity C/cm2 = 1.3 +/- 0.2 microF/cm2, and length constant lambda = 900 +/- 40 micron; and 2) for vein, Vm = -66 +/- 3 mV, Rin = 450 +/- 25 M omega, tau m = 19 +/- 2 ms, C/cm2 = 1.0 +/- 0.1 microF/cm2, and lambda = 1,300 +/- 200 micron. The values calculated for a short cable and the observed change of the membrane potential as a single exponential, in response to hyperpolarizing pulses of current, both indicate that the cell membrane behaves as an isopotential surface. With hyperpolarizing pulses, both cell types gave linear voltage-current (V-I) relationships with a constant slope, Rin. On the other hand, depolarizing pulses elicited outward rectification. Voltage-clamp experiments show an outward voltage-dependent K+ current (IK) when the cell membrane is depolarized beyond approximately equal to -40 mV from holding levels approximately equal to -60 mV. Maximum slope conductances were of approximately 120 microS/cm2. Blocking of K+ channels with tetraethylammonium ions did not unmask an inward current. These results indicate that VSMC from rat caudal artery and vein in culture have K+ channels responsible for the graded depolarization of the cell membrane in response to an electrical stimulus. Furthermore, this experimental approach seems to be adequate to further study the electrical responses of VSMC from vessels at distinct stages of development, and to follow these responses as the cells change in a defined environment.