The dynamic breakdown of heart cell membranes exposed to ramp increases in transmembrane potential

The role of electroporation in high-energy shock of cardiac muscle was investigated. Membrane patches of single frog ventricular cells drawn into glass micropipettes were exposed to relatively large transmembrane potentials using a custom-built whole-cell patch clamp unit. The current through the pipette was measured during the application of voltage ramps, which enabled the observation of rapid changes in membrane impedance due to electrical breakdown. The results show that the dynamic electrical breakdown of heart cell membrane involves threshold levels of transmembrane potential above which there exist a period of reversible membrane instability and a rapid, irreversible increase in membrane permeability. The data suggest that the threshold voltages for the onset of these events are independent of the polarity of the applied voltage ramp. The data support the theory that membrane breakdown is a function of transmembrane potential, i.e. a process of electroporation. The advantage of using ramp waveforms for membrane breakdown studies is discussed