In general, independency of individual channel behaviour seems to be admitted, perhaps because the number of the channel that opens simultaneously in a multi-channel patch is identified with that estimated by the binomial distribution theory. The aim of this study was to confirm whether there is some inter-relationship between channels.

Simultaneous recordings of the single channel currents of neighbouring BK channels were carried out from enzymatically dispersed smooth muscle cells (obtained from humanely killed guinea-pigs) using a theta-type double-barrelled patch electrode, in the cell-attached configuration and voltage-clamp mode. Both the solutions of the organ bath and the patch electrode were the same (mM): KCl 140, CaCl₂ 2.0, MgCl₂ 1.2 and Hepes 10.5. Under the conditions in which one barrel (A patch) of an electrode was fixed at +40 mV of patch potential, another barrel (B patch) was stepwisely varied between -80 and +80 mV, where open events of BK channels were observed in both patches. The timing for switching the channel from open to closed or from closed to open coincided between two patches, in some proportion. Events briefer than 1 ms were ignored. The number matching in which the time lag is equal to or less than 0.2 ms was counted. As a typical example, the results obtained when the B patch was clamped at -80 mV is shown as follows: probabilities of matching (number of matching/total number of open and closed in the observation time) were 18.9 and 16.4 % for A and B patches, respectively. On the other hand, the matching necessarily has to be made without any functional interaction between the two patches. The probability of such a matching was 7.6 and 8.4 % for A and B patches, respectively, showing that the former is at least 2.4 times larger than the latter. The direction of the switch did not exert remarkable influence. For the open life time of the channel, no positive (simultaneously open or closed in both patches) nor contrary (open in one patch and closed in the other patch) correlation was seen. In order to observe directly the effects of current through a channel on the behaviour of neighbouring channels, a rectangular electrical current of 15 or 30 pA in amplitude and 10 ms in duration was applied through one barrel of the electrode where the giga ohm seal was not formed, although the other barrel had the seal and was kept at -80 mV of clamping voltage. Under such conditions, the probability of matching between the open or closed BK channels and the ‘on’ or ‘off’ of the applied currents was 6.2 %. The probability of the matching expected statistically was 1.5 %. Also, no difference in the open probability was seen between the presence or absence of current application.

These results suggest that there is some interaction between neighbouring channels, probably by the deflection of channel current.