The resting membrane parameters of human intercostal muscle at low, normal, and high extracellular potassium

Membrane parameters at the respective resting potentials in low, normal, and high extracellular potassium solutions were determined in intercostal muscle fibers from 15 patients with no known neuromuscular disease. In synthetic interstitial fluid (normal potassium concentration 3.5 mmol/liter), we found the following mean values: resting membrane potential RP = -83.3 mV, space constant lambda = 2364 micron, fiber diameter d = 49.3 micron, fiber input resistance Rin = 795 k omega, specific membrane capacitance Cm = 4.7 muF/cm2, and specific membrane resistance Rm = 5970 omega X cm2. The specific membrane conductance was gm = 168 muS/cm2, 76% of it being chloride conductance, 24% being potassium conductance. The dependence of the membrane parameters on the extracellular potassium concentration followed the predictions by the constant field theory. There was no indication of active chloride transport. The resting membrane conductance decreased with temperature with a Q10 of 1.3. Excitability parameters were nearly independent of temperature between 37 and 27 degrees C.