Field induced membrane potential changes in small regions of guinea pig papillary muscles

Optical potential mapping with very high temporal and spatial resolution allowed a detailed investigation of membrane potential changes in guinea pig papillary muscle´s during field stimulation. Using the fluorescent potential sensitive dye di-4-ANEPPS and laser excitation we have investigated the depolarization phases in areas within a small region (<1 mm) at the tip of the muscle. Electrical pulses of various field strength, applied perpendicular to the fiber axis, caused complex depolarization processes with time delays up to more than 5 ms (the pulse duration). With increasing pulse amplitudes (up to 13.5 V/cm) field induced local membrane polarizations became more and more prominent and influenced especially the hyperpolarized areas. The pronounced time lags, occurring even in such small regions may increase the risk of refibrillation in a defibrillation therapy