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

Abstract

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 γLD = 2364 μm, fiber diameter d = 49.3 μm, fiber input resistance R_in = 795 KΩ, specific membrane capacitance C_m = 4.7 μF/cm², and specific membrane resistance R_m = 5970 Ω·cm². The specific membrane conductance was g_m = 168 m̈S/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°C.