Voltage clamp of rat and human skeletal muscle: measurements with an improved loose-patch technique.
Intact fibres of human intercostal and rat omohyoid muscles were studied at 23 degree C with a loose-patch voltage-clamp technique that employed two concentric micropipettes to electrically isolate small-diameter (10-15 microns) patches of sarcolemma. This method allows investigation of membrane excitability under highly physiological conditions. Step depolarizations to 0 mV elicited sodium inward currents that reached peak values of up to 20 mA/cm2 within 250 microseconds, and then declined. In human muscle, the reversal potential (ENa) was approximately 40 mV, and maximal conductances (GNa) ranged from 44 to 360 mS/cm2. In rat muscle, ENa was 42 mV and GNa ranged from 100 to 250 mS/cm2. Sodium channels in rat and human muscle were indistinguishable in most aspects of their kinetic behaviour and voltage dependence. Outward potassium currents were small by comparison (usually less than 2 mA/cm2) and saturated at positive potentials. The maximum potassium conductance (GK) ranged from 0 to 19 mS/cm2 (human) and from 4 to 12 mS/cm2 (rat muscle).
D000200:Action Potentials; D000328:Adult; D000818:Animals; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D006801:Humans; D066298:In Vitro Techniques; D007473:Ion Channels / Q000502:physiology; D008297:Male; D008564:Membrane Potentials; D008875:Middle Aged; D009132:Muscles / Q000502:physiology*; D011188:Potassium / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000502:physiology
D007473:Ion Channels; D012964:Sodium; D011188:Potassium