Cation regulation in the smooth muscle of frog stomach.

Abstract

Cation composition of frog smooth muscle cells was investigated. Fresh stomach muscle rings resembled skeletal muscle, but marked Na gain and K loss followed immersion. Mean Na (49.8-79.7 mM/kg tissue) and K (61.8-80.1 mM/kg tissue) varied between batches, but were stable for long periods in vitro. Exchange of 6-30 mM Na/kg tissue with (22)Na was extremely slow and distinct. Extracellular water was estimated from sucrose-(14)C uptake. Calculated exchangeable intracellular Na was 9 mM/kg cell water, and varied little. Thus steady-state transmembrane cation gradients appeared to be steep. K-free solution had only slight effects. Ouabain (10(-4)M) caused marked Na gain and reciprocal K loss; at 30 degrees C, Na and K varied linearly with time over a wide range of contents, indicating constant net fluxes. Net fluxes decreased with temperature decrease. (22)Na exchange in ouabain-treated tissue at 20-30 degrees C was rapid and difficult to analyze. The best minimum estimates of unidirectional Na fluxes at 30 degrees C were 10-12 times the constant net flux; constant pump efflux may explain these findings. The rapidity of Na exchange may not reflect very high permeability, but it does require a high rate of transport work.