Control of the contractile mechanism of smooth and cardiac muscle

Abstract

The glycerated stomach muscle of the frog and the aorta of the turtle had contractile properties only if the muscles were washed in dilute solutions before storage in glycerol Such muscles contracted in ATP solutions at Ca ion concentrations above 4.10 -7 M, but the glycerated frog''s ventricle produced more than half its maximal tension at the lowest concentrations attainable by chelating agents. When fully contracted in an ATP solution EGTA produced very incomplete relaxation, but tension dropped further with increasing concentrations of ATP. The tension of smooth and cardiac muscle produced in ATP solutions by the addition of Ca was proportional to [Ca++] over a large range. The steepness of the rise Increased markedly with pH.