Inward rectification in frog skeletal muscle fibres and its dependence on membrane potential and external potassium.

Experiments were carried out using a voltage-clamp technique to investigate the dependence of inward rectification on membrane potential and on the equilibrium potential for K+, changed either by changing Ko or changing Ki. 2. The relationship between gK, the potassium chord conductance, and membrane potential depended on membrane potential and Ko, but not on Ki. 3. Under hyperpolarization, K currents increased with time, but instantaneous current-voltage relations also showed inward rectification. The time constants for activation fell with hyperpolarization, e -fold for an 18 mV change in membrane potential. 4. The time constants for activation depended on Ko but not on Ki. 5. Under depolarization, the activation of K currents was partly reversed, but between activation and membrane potential, determined from two-pulse experiments, also appeared to depend on Ko but not on Ki. 5. Under depolarization, the activation of K currents was partly reversed, but between activation and membrane potential, determined from two-pulse experiments, also appeared to depend on Ko but not on Ki. 6. The rate of activation of K currents under hyperpolarization had a Q10 of 2.64 +/- 0.08 (n = 5). Currents, measured per unit length, increased with temperature, with a Q10 of 1.66 +/- 0.11 (n = 5).