Characterization of the stretch-activated chloride channel in isolated human atrial myocytes

Macroscopic and unitary currents through stretch-activated Cl- channels were examined in isolated human atrial myocytes using whole-cell, excised outside-out and inside-out configurations of the patch-clamp technique. When K+ and Ca2+ conductances were blocked and the intracellular Ca2+ concentration ([Ca2+]i) was reduced, application of positive pressure via the pipette activated membrane currents under whole-cell voltage-clamp conditions. The reversal potential of the current shifted by 60 mV per 10-fold change in the external Cl- concentration, indicating that the current was Cl- selective. The current was inhibited by bath application of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and 9-anthracenecarboxylic acid (9-AC). beta-Adrenergic stimulation failed to activate a Cl- current. In single channel recordings from outside-out patches, positive pressure in the pipette activated the unitary current with half-maximal activation of 14.7 mm Hg at +40 mV. The current-voltage relationship of single channel activity obtained in inside-out patches was linear in symmetrical Cl- solution with the averaged slope conductance of 8.6 +/- 0.7 pS (mean +/- SD, n = 10). The reversal potential shift of the channel by changing Cl- concentration was consistent with a Cl- selective channel. The open time distribution was best described by a single exponential function with mean open lifetime of 80.4 +/- 9.6 msec (n = 9), while at least two exponentials were required to fit the closed time distributions with a time constant for the fast component of 11.5 +/- 2.2 msec (n = 9) and that for the slow component of 170.2 +/- 21.8 msec (n = 9). Major changes in the single channel activity in response to pressure were caused by changes in the interburst interval. Single channel activity was inhibited by DIDS and 9-AC in a manner similar to whole-cell configuration. These results suggest that membrane stretch induced by applying pressure via the pipette activated a Cl- current in human atrial myocytes. The current was sensitive to Cl- channel blockers and exhibited membrane voltage-independent bursting opening without sensitive to beta-adrenergic stimulation.