Effects of High Potassium and Caffeine Exposure on Activities of Ca 2+-Dependent and Ca 2+-Independent Protein Kinase C in Frog Skeletal Muscle

Abstract

With the use of histone III-S as a protein kinase C (PKC) substrate, the activities of total and Ca 2+-independent PKC in frog skeletal muscle were measured, and their difference is designated Ca 2+-dependent PKC. In resting muscle, the total PKC was almost equally associated with the cytosol and membrane, and the ratio of membrane to cytosol PKC was about 1. However, the distribution of PKC was subtype dependent. About 60% of Ca 2+-dependent PKC was located in the cytosol, whereas Ca 2+-independent PKC was mainly associated with the membrane. High potassium exposure not only caused a significant translocation of Ca 2+-dependent PKC from the cytosol to the membrane, but also changed the distribution of Ca 2+-independent PKC, although to a lesser extent. However, in the preparations exposed to caffeine, the translocation of PKC occurred only in a Ca 2+-dependent subtype. In addition, the biphasic change in membrane-associated PKC seen in high K + exposed muscles was absent with caffeine treatment. The possible mechanisms of these differences are discussed.