Ion-channel open probability ($P_O$)

The probability that an ion channel is in a conducting open state under specified conditions. For N equivalent channels, each carrying open-state electric current i, the mean total electric current is $N{P}_{O}i$. An ensemble open fraction and the fraction of time one channel remains open coincide under suitable stationary and ergodic assumptions. A two-state ion-channel gating model is one model of this probability, not its definition.