Effect of pyrophosphate on the shortening of muscle-fibre models in presence of adenosine triphosphate.

Abstract

WEBER1 has shown that pyrophosphate in fairly high concentrations (20 mM or above) produces relaxation in single glycerinated muscle fibres which have shortened or developed tension in adenosine triphosphate. He found, however, that it had this effect only when adenosine triphosphate was absent, shortening proceeding normally in presence of the latter. This contrasts markedly with the lengthening effect of the so-called Marsh factor, which is a protein found in aqueous extracts of muscle2,3. The latter effect manifests itself only in the presence of adenosine triphosphate and magnesium chloride (2–8 mM) and is inhibited3,4 by traces of calcium chloride (0.2 mM).