Electroporation induced by high-strength electrical fields has long been used to investigate membrane properties and facilitate transmembrane delivery of molecules and genes for research and clinical purposes. In the heart, electric field-induced passage of ions through electropores is a factor in defibrillation and postshock dysfunction. Voltage-clamp pulses can also induce electroporation, as exemplified by findings in earlier studies on rabbit ventricular myocytes: Long hyperpolarizations to ≤−110 mV induced influx of marker ethidium and irregular inward currents that were as large with external NMDG+ as Na+. In the present study, guinea pig ventricular myocytes were bathed with NMDG+, Na+ or NMDG+ + La3+ solution (36°C) and treated with five channel blockers. Hyperpolarization of myocytes in NMDG+ solution elicited an irregular inward current (I ep) that reversed at −21.5 ± 1.5 mV. In myocytes hyperpolarized with 200-ms steps every 30 s, I ep occurred in “episodes” that lasted for one to four steps. Boltzmann fits to data on the incidence of I ep per experiment indicate 50% incidence at −129.7 ± 1.4 mV (Na+) and −146.3 ± 1.6 mV (NMDG+) (slopes ≈−7.5 mV). I ep amplitude increased with negative voltage and was larger with Na+ than NMDG+ (e.g., −2.83 ± 0.34 vs. −1.40 ± 0.22 nA at −190 mV). La3+ (0.2 mM) shortened episodes, shifted 50% incidence by −35 mV and decreased amplitude, suggesting that it inhibits opening/promotes closing of electropores. We compare our findings with earlier ones, especially in regard to electropore selectivity. In the Appendix, relative permeabilities and modified excluded-area theory are used to derive estimates of electropore diameters consistent with reversal potential −21.5 mV.
The Journal of Membrane Biology – Springer Journals
Published: Nov 21, 2010
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