Further Investigations on the Effect of Adenosine Triphosphate and Related Phosphorus Compounds on Isolated Striated Muscle Fibres

Abstract

Summary. In agreement with previous results it was found that ATP prepared in different ways initiates contraction and changes birefrigence when applied in minute amounts to isolated striated muscle fibres of the frog. ATP is evenly distributed in the muscle and not localized specially in the region of the motor end plate. Lack or excess of calcium just as excess of magnesium increase the threshold value for ATP. While adenosine alone is without effect, it changes the contracture‐like effect of pyrophospate to a normal tetanus‐like contraction. Inosine triphosphate, thrice as active as ATP in initiating contraction is without effect on birefringence. Creatine phosphate has no effect on striated muscle, thus establishing the breakdown of ATP as the reaction nearest in time to contraction. Creatine phosphate + adenylic acid can replace ATP in the release of contraction and causes a reversible fall in birefringence. The time of restitution, however, is considerably longer than with ATP. Acetyl phosphate is without effect. Acetylcholine abolishes the effect of ATP on birefringence while it does not affect release of contraction. In denervated muscle previous application of acetylcholine prevents release of contraction by ATP. Contraction in denervated muscle is not accompanied by the slow changes in birefringence.