Comparison of electrical properties of middle cerebral and mesenteric artery in cat

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Abstract
Some electrophysiological properties of the smooth muscle within the middle cerebral artery of the cat were recorded with glass microelectrodes and compared to those of mesenteric and coronary arteries of the same animal. A significantly higher resting membrane potential (Em) in the middle cerebral arteries (-70 mV) was demonstrated when compared to the mesenteric (-49 mV) and coronary (-58 mV) arteries. When the Em was measured at different values of extracellular K, the middle cerebral artery depolarized with a maximum slope of 58 mV/decade vs. 36 mV/decade in the mesenteric arteries. The input resistance was less (6 M.OMEGA.) in the middle cerebral artery than in the mesenteric artery (10 M.OMEGA.) suggesting that K conductance (GK) is higher in the middle cerebral artery. Upon short exposure to ouabain (5 min) the middle cerebral artery depolarized by 20 mV vs. 8 mV in the mesenteric artery. An elevated GK and greater electrogenic Na-K pump may contribute to the steeper slope of the Em vs. log(K]o curve in the middle cerebral artery compared to the mesenteric artery. Spontaneous electrical activity was recorded in the middle cerebral artery upon depolarization with K, but only graded depolarizations were recorded in the mesenteric artery. Serotonin (10-6 M) depolarized the smooth muscle of the middle cerebral arteries and produced spontaneous electrical activity which could be blocked by verapamil. Marked differences in the electrical properties of the smooth muscle cells of the middle cerebral artery compared to the mesenteric artery are demonstrated.