Abstract

The effects of 3.67 mM procaine on nicotine-induced tension and Ca⁴⁵ movements and on nicotine-C¹⁴ movements are ascertained in frog sartorius muscles at pH 7.40 and pH 8.40. The nicotine contracture is augmented by procaine at pH 8.40 and inhibited by procaine at pH 7.40. Contractures also occur at pH 8.40 when muscles are exposed to procaine alone. Residual Ca⁴⁵ uptake (after a 120-min washout) is significantly increased when muscles at pH 8.40 are treated with procaine alone or when procaine is added to Ringer's solutions containing 0.415 mM nicotine, but not when procaine is added to solutions containing 2.50 mM nicotine. Residual Ca⁴⁵ uptake is inhibited at pH 7.40 when procaine is added to solutions containing 10 mM nicotine. Ca⁴⁵ efflux into a Ca-free Ringer's solution containing 4 mM ethylenediamineteraacetic acid is increased by procaine at pH 8.40 but not at pH 7.40. Procaine decreases uptake and increases efflux of nicotine-C¹⁴ whereas iodoacetic acid increases uptake and decreases efflux of nicotine-C¹⁴. Both of these agents alter the DMO-C¹⁴ space and the resultant calculated intracellular pH values in a manner which indicates that this action could account for their effects upon nicotine-C¹⁴ distribution. The ionized form of procaine appears to be important for inhibition of nicotine-induced contracture and residual Ca⁴⁵ uptake as well as for increased intracellular pH levels. The presence of nonionized procaine molecule can be correlated with contracture and increased residual Ca⁴⁵ uptake in a manner similar to that of nonionized nicotine.