THE EFFECTS OF METHOXAMINE UPON THE MEMBRANE RESTING AND ACTION POTENTIALS OF THE GUINEA PIG'S VENTRICULAR MUSCLE FIBRES

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Abstract
Using the glass capillary ultramicroelectrode, the effects of methoxamine upon the membrane resting and action potentials of the ventricular muscle fibers of the guinea pig were examined. Methoxamine, in doses of 100-200 [mu]g/ml, reduced the maximum rate of rise of the rising phase of the action potential considerably without producing any appreciable change in the magnitude of the membrane resting and action potential. The duration of the action potential was moderately prolonged. Concurrently with the changes in the membrane potential, there was observed diminished contraction. In order to get some information about the permeability of the resting membrane, the chronaxie for the square wave pulses stimulation was determined. No remarkable change in the chronaxie was observed. The discussion was presented concerning the underlying mechanisms of the change in the pattern of the membrane potential. The possibility of correlating these changes with the diminished contraction was discussed.