MECHANISMS OF SMOOTH MUSCLE RELAXATION THROUGH THE ANODAL CURRENT STIMULATION.
HIROSHIMA UNIV (JAPAN) DEPT OF PHYSIOLOGY
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The comparative physiological method was combined with the electrophysiological method in an attempt to resolve the problems related to the mechanisms of relaxation of the involuntary muscle system. The effect of sodium ion on the mammalian smooth muscles, vertebrate myocardium, and invertebrate myocardium has been compared since 1962. Effect of higher sodium concentration on the myocardium was obtained by using the skate myocardium without changing the osmotic pressure of the bath. The results of this study will be published in the Journal General Physiology. A continuation of this research is in progress by studying the effect of Ca on the myocardium. In the skate myocardium, the elevation in action potential by increasing Ca was found to be caused by the increased availability of Na carrier and probably not by the direct inflow of Ca into the cell. On the other hand, in the invertebrate myocardium such as molluscus, Ca appears to play a very important role for the initiation of action potential. The heart muscle of the oyster can continue to contract spontaneously in Na free solution. Amplitude of action potential of the oyster myocardium increased 29 mV by a 10 fold increase in extracellular Ca concentration. Spontaneous activity was not diminished in a relatively high concentration of puffertoxine but was inhibited by the administration of manganese ion. All these facts indicate that the inward current may be carried by Ca ion in the extreme condition in this heart muscle. In connection with this study, the ionic concentrations of intracellular Na and K were studied in the skate myocardium and similar measurements are being made on other muscles. Author
- Anatomy and Physiology