EFFECT OF CALCIUM ON SKELETAL MUSCLE MEMBRANE AFTER TREATMENT WITH PHOSPHOLIPASE C

The effects of phospholipase C on the muscle membrane were studied by the recording of the resting membrane potential, the input resistance and the action potential generation in single fibres of the isolated extensor digitorum longus and soleus muscles of the rat. Incubation with phospholipase C abolished spike generation, depolarized the fibres by 15–20 mV and increased the ionic permeability of the membrane as shown by a fall of about 40 per cent of the “input” resistance. Removal of the enzyme by washing the preparation with Krebs‐Ringer solution did not restore membrane exitability, the resting membrane potential nor the input resistance of the fibres. When the external calcium concentration was raised from the normal 2 mM to 15 mM the muscle fibres repolarized and action potentials with a reduced rate of rise and amplitude were recorded. No recovery of the input resistance occurred. When the calcium concentration was brought back to 2 mM the fibres again depolarized and became inexcitable. Potassium (10 or 15 mM), caesium (10 mM) or rubidium (6 mM) antagonized the aforementioned effects of 15 mM calcium. It was concluded that phospholipase C irreversibly affected the muscle membrane and that an increase in the external calcium ion concentration only functionally restored some of the membrane properties, i.e., spike generation and the resting membrane potential. The results support the view that the hydrophilic head of certain membrane phospholipids is connected with passive ion transport in the electrogenic membrane. © 1968 Scandinavian Physiological Society