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Am J Physiol Heart Circ Physiol 273: H2817-H2825, 1997;
0363-6135/97 $5.00
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Vol. 273, Issue 6, H2817-H2825, December 1997

Dose-dependent reduction of cardiac transmembrane potential by high-intensity electrical shocks

Michel Neunlist1 and Leslie Tung2

1 Department of Physiology, School of Veterinary Medicine of Hannover, 30173 Hannover, Germany; and 2 Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, Maryland 21205

Cardiac tissue dysfunction can result from high-intensity electrical shocks and is manifested as changes in transmembrane potential (Vm). Ten-millisecond shock pulses (SPs) of varying intensity and polarity were applied to frog ventricle in diastole, and Vm was quantified directly under the stimulating electrode by an optical method using voltage-sensitive dye. As SP intensities were increased, the shock-induced action potential (AP) plateau and AP amplitude (APAs) decreased sigmoidally toward 75-85% of the control AP amplitude (APAc) and zero, respectively. APAs was shifted toward lower current densities for anodal compared with cathodal SPs (half-maximal values 185 and 238 mA/cm2, respectively; P = 0.02). Recovery of APAs was marginally significant 1 s after SP delivery (P = 0.063). The peak change in Vm during SP (across all intensity levels) was -200% APAc for anodal and +125% APAc for cathodal pulses. In conclusion, we show that SP reduces APA in a sigmoidal fashion at strengths >10-20 × diastolic threshold and is more deleterious for anodal polarities.

cardiac tissue; voltage-sensitive dye; anodal shock; cathodal shock; extracellular electrode; electroporation


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