QUININE CONTRACTURES AND Ca⁴⁵ MOVEMENTS OF FROG SARTORIUS MUSCLES AS AFFECTED BY pH

¹ Division of Physiology, Institute for Muscle Disease, New York, New York

Raising the pH of the experimental medium from 6.2 to 8.2 enhances the capability of quinine (0.1-5 mM) to cause contracture in frog sartorius muscles and to increase the rate of release of Ca⁴⁵ during the efflux of the Ca⁴⁵ slow component of these muscles. Since raising the pH causes a relative increase of the uncharged and therefore penetrating form of quinine, and since Carvalho (J. Gen. Physiol. 52: 622-642, 1968) has shown that quinine causes release of Ca⁺⁺ from isolated reticulum, we infer that the observed increase in Ca⁴⁵ 1 efflux represents release of Ca⁺⁺ from the in situ sarcoplasmic reticulum and that the contracture results from this release. The effects of quinine (2mM), unlike similar ones of caffeine, are not blocked by procaine (2mM), indicating, in conformance with Carvaiho's results, that the two drugs cause release of Ca⁺⁺ from reticulum by different mechanisms.