Ionic mechanisms underlying the negative slope formation of the inward-rectifying potassium background current in ventricular cell of guinea-pig heart.

Kinetics of the inward-rectifier K+ channel (IK rec), which is the major fraction of the background potassium current (iK1) in cardiac cells, were studied in enzymatically-dispersed cells of guinea-pig ventricle. Currents flowing through IK rec channel were recorded using the cell-attached patch clamp technique with pipettes containing 150 mM or 75 mM K+. Steady state unitary currents and ensemble averaged currents of the channel were analysed. From the analyses, it was indicated that the kinetics of IK rec channel at potentials positive to EK-20 mV are determined mostly by activation gate. The activation gate of the channel follows the first order reaction between one open and one closed states and depends on shift of the membrane potential from the potassium equilibrium potential. The calculated macroscopic current flowing through the channel during the activation process showed prominent inward-reactification and formed a negative conductance region. In conclusion, the properties of iK1 depend on the activation kinetics of IK rec channel.