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.Po) 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.Po were -9.3 mV and +8.9 mV, and maximum values of n.Po at positive potentials were 1.23 and 0.33. At potentials > or = 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.
Michelakis
E
E
Division of Neurological Surgery, University of Maryland Hospital, Baltimore 21201-1595.
Tewari
K
K
Simard
J M
JM
D000818:Animals; D001160:Arterioles / Q000502:physiology*; D001488:Basilar Artery / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D002531:Cerebellum / Q000098:blood supply; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D009543:Nifedipine / Q000494:pharmacology
D015220:Calcium Channels; D009543:Nifedipine