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 ce lls from cerebral precapillary arterioles and basilar artery of guinea pig. Patches were studied without Ca2+ channel activators in the pipe tte solution. In both preparations, a 23 pS channel (40 mM Ba2+) sensi tive to block by nifedipine was identified. In arteriolar but not in b asilar 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 variou s potentials were fit to a Boltzmann function. For the arteriolar patc hes (n=5) and for patches from basilar artery (n=5), the midpoint pote ntials for the voltage dependence of n.P-o were -9.3 mV and +8.9 mV, a nd maximum values of n.P-o at positive potentials were 1.23 and 0.33. At potentials greater than or equal to 0 mV, the average for the maxim um 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 op enings. Our data indicate that Ca2+ channel activity is likely to be m ore prominent near resting membrane potentials in arteriolar cells tha n in basilar artery cells.