Figure 1.

Heterogeneity of K_ACh channel gating in neonatal rat atrial myocytes. Two examples of single-channel activity recorded from cell-attached patches in the presence of 1 μM ACh are shown in A and B to illustrate the kinetic heterogeneity of channel gating encountered in our experiments. The membrane potential of the patch was held at −90 mV in both cases. In this and all figures, the downward deflections correspond to inward currents. All-points and open-time histograms generated from the data shown in A and B are presented on the right. The all-points histograms were fitted by the sum of two Gaussian functions to determine the channel open probability, P _o. The P _o value obtained from the 20-s record is 0.013 in A and 0.297 in B. The open time distributions were fitted by the sum of two exponential components. The time constants of the fast and slow components are τ_o1 = 1.56 ms (83.6%) and τ_o2 = 7.50 ms (16.4%) in A and τ_o1 = 1.22 ms (52.1%) and τ_o2 = 7.54 ms (47.9%) in B. The time constants of the fast and slow components showed little variations from one experiment to another; however, the relative areas under the individual exponents were different.