The action potential and underlying ionic currents in proximal rat middle cerebral arterioles.
The active and passive electrical properties of isolated segments (length 120-220 microns, diameter 60-150 micron) of proximal rat middle cerebral arterioles (less than 1 mm from parent artery) were analysed using a single-electrode current or voltage clamp. The voltage response to a current step exhibited an exponential time course. The mean resistance and time constant was 102 M omega and 265 ms corresponding to approximate specific resistance and capacitance of 60 k omega/cm and 4 micro F/cm2. Membrane resistance was constant in the range -55 to -80 mV. At potentials more negative than -80 mV there was a decrease in membrane resistance resulting in activation of an inward rectifier. At membrane potentials less negative than -50 mV the membrane resistance decreased; larger depolarizations (greater than -40 mV) initiated small regenerative responses. External application of tetraethylammonium chloride caused membrane depolarization (10-15 mV), spontaneous discharge of action potentials and rhythmic arteriolar constriction. Action potentials studied with the membrane held at -60 mV had a large rapid depolarizing component, an after-depolarization and a small slower after-hyperpolarization. Tetrodotoxin (TTX) had no effect on the action potential. However, both the fast and slow components of the action potential were suppressed by extracellular removal of calcium ions and/or addition of cobalt ions, nifedipine or verapamil. Voltage-clamp studies demonstrated an inward rectifying current at membrane potentials more negative than -80 mV. At depolarized potentials at least four separate currents were activated; two separate calcium currents and two outward currents.
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Hirst
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Silverberg
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van Helden
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001160:Arterioles / Q000502:physiology; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002536:Cerebral Arteries / Q000502:physiology; D003035:Cobalt / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D051381:Rats; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D007473:Ion Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D003035:Cobalt; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D002118:Calcium