Activators of protein kinase C induce myotonia by lowering chloride conductance in muscle.

Certain phorbol esters and bryostatin 1, known activators of protein kinase C, were found to induce, in genetically normal muscle, an electrical membrane instability leading to unscheduled series of action potentials. Like in hereditary myotonias of man, goat and mouse, these symptoms were caused by a drastically lowered sarcolemmal chloride conductance. Our results indicate that the chloride channels of mammalian muscle may be subject to modulation by the protein kinase C-diacylglycerol system.