Calcium channel currents in vasculr smooth muscle cells cultured in defined media

Experimental conditions which retain the biochemical properties of rat aortic smooth muscle cells (SMC) for several days in culture have been established (Hedin et al., J. Cell Biol. 107: 307-319). To test whether the electrophysiological properties of these cells are maintained as well, we compared the calcium channel currents carried by barium in freshly isolated rat aortic SMC to those of SMC plated on collagen type IV and incubated for up to three days in defined media (F12) supplemented with 0.1% BSA, 50 μg/ml ascorbic acid, 10 mM Na-HEPES, and 10 mM Na-TES. Using the whole-cell mode of the patch clamp technique, the cells were clamped at -80 mV and stepped for 75 ms to test potentials up to +50 mV. Both preparations expressed non-inactivating barium currents which activated at -20 mV and were maximal at +15 to +20 mV. Barium current density (defined as the maximal current divided by the cell capacitance) in the cultured cells was four fold greater than the current density in the freshly dissociated cells (100±1.6 pA/μm² (n=5, ±SE) and 2.5 ±0.6 pA/μm² (n=7; ±SE), respectively). It is yet unclear whether the difference in current density results from transient damage induced by the isolation procedure or from enhanced expression of channels in culture. Regardless, since both preparations appear to express the same class of calcium channels, the cultured cells may be suitable for long term studies on electrophysiological properties of vascular SMC.