Calcium channels in smooth muscle cells from cerebral precapillary arterioles activate at more negative potentials than those from basilar artery

We compared Ca²⁺ channels in cell-attached patches of smooth muscle cells from cerebral precapillary arterioles and basilar artery of guinea pig. Patches were studied without Ca²⁺ channel activators in the pipette solution. In both preparations, a 23 pS channel (40 mM Ba²⁺) sensitive to block by nifedipine was identified. In arteriolar but not in basilar artery patches, channel activity was recorded without apparent inactivation at potentials of –40 to –20 mV. Values for the number of channels in a patch x probability of channel opening (n·P_o) at various potentials were fit to a Boltzmann function. For the arteriolar patches (n=5) and for patches from basilar artery (n=5), the midpoint potentials for the voltage dependence of n·P_o were –9.3 mV and +8.9 mV, and maximum values of n·P_o at positive potentials were 1.23 and 0.33. At potentials 0 mV, the average for the maximum number of superimposed openings in basilar artery patches was 1.7 (n=17) and in arteriolar patches was 6.5 (n=6). For both preparations, histograms of channel open times at –10 mV required two time constants, 0.48 and 3.95 ms, and the shorter open state accounted for 88% of openings. Our data indicate that Ca²⁺ channel activity is likely to be more prominent near resting membrane potentials in arteriolar cells than in basilar artery cells.