The stretch-activated potassium channel TREK-1 in rat cardiac ventricular muscle

Cardiac TREK-1 like potassium channels play an important role in the function of cardiomyocytes. A novel low-conductance TREK-1 like potassium channel and a high-conductance TREK-1 like potassium channel in rat cardiomyocytes are described in this thesis. The biophysical properties of the two cardiac TREK-like channels were similar to those of TREK-1a or TREK-1b channels expressed in HEK293 cells, which both displayed a low- and a high-conductance mode. Using cell-specific RT-PCR we found strong expression of a splice variant of rat TREK-1, denoted TREK-1b, in which the N-terminus is extended by 15 amino acids compared to the 'classical' TREK-1a channel protein. Immunohistochemistry with antibodies against TREK-1 showed localization of the channel in longitudinal stripes at the external surface membrane of cardiomyocytes. When the cardio-myocytes were mechanically stretched using a glass stylus, an outwardly rectifying K+ current component could be detected in whole-cell recordings. In single-channel recordings with symmetrical high K+ solution, two TREK-like channels with 'flickery-burst' kinetics were found: a ‘high-conductance?K+ channel (1325 pS at positive potentials) and a novel ‘low-conductance?channel (415 pS at positive potentials). The low-conductance channel could be activated by negative pressure in inside-out, positive pressure in outside-out patches, intracellular acidification and arachidonic acid. Its open probability was strongly increased by depolarization, due to decreased duration of gaps between bursts. The biophysical properties of the two cardiac TREK-like channels were similar to those of TREK-1a or TREK-1b channels expressed in HEK293 cells, which both displayed a low- and a high-conductance mode. Our results suggest that the TREK-like channels found in rat cardiomyocytes may reflect two different modes of TREK-1. The current flowing through these mechano-gated channels may serve to counterbalance the inward current flowing through stretch-activated non-selective cation channels during the filling phase of the cardiac cycle and thus to prevent the occurrence of ventricular extrasystoles