Potassium contractures and mechanical activation in rat skeletal muscle: effects of multivalent cations, temperature and tetracaine

1 The effects of cations, temperature and tetracaine on potassium-induced contractures of rat soleus and extensor digitorus longus (e.d.l.) muscles were investigated. 2 In the soleus, the threshold for the potassium contracture was lower (10–20 vs 20–40 mm), the peak amplitude was up to fourteen times larger, and the time course was about one half that in the e.d.l. muscle. The extent of inactivation of a test potassium contracture was directly related to the concentration of potassium in the conditioning solution and the period of exposure. 3 Removal of calcium reduced the amplitude and time course of potassium contractures in both preparations. Addition of cobalt (10 mm) reduced the amplitude but prolonged the time course of contractures. 4 Exposure of muscles to tetracaine (10−5-10−6m for 30 min) increased, but higher concentrations reduced, the amplitude of potassium contractures. When present for one minute, tetracaine (1 mm) moved the potassium activation curve to higher, and the potassium inactivation curve to lower, potassium concentrations.