Typical current from a multiple-channel patch. (A) The outside-out patch current activated by 10 μM ATP recorded at -120 mV from a Xenopus oocyte. The data were sampled at 10 kHz and filtered at 5 kHz. There are at least three channels active in this patch as indicated by the open level of current. There are a surprising number of what appear to be nearly simultaneous openings and closings, some of which are marked by arrows. These occurrences are the indication of channel interactions. The convention in this paper is that inward currents are downward. (B) The all-points amplitude histogram of currents from panel A (0.15 pA/bin). The distribution was fit by a sum of four Gaussians (lines), with means of 0, 4.1, 7.9 and 11.9 pA, representing the closed, 1st, 2nd, and 3rd open levels. The open channel noise of each level was ~1.2 pA. The probabilities, P(k)exp, that all channels are closed, one, two, and three channels are open from histogram are 0.210, 0.487, 0.270, 0.027, respectively in this patch. (C) Comparison of P(k)exp with P(k)binomial from the binomial distribution (Eq. 5). The ratio of P(k)exp/P(k)binomial increases with increasing k.