Structure related membrane polarizations in field stimulated guinea pig papillary muscle

We have performed optical potential mapping with very high temporal and spatial resolution in guinea pig papillary muscles during the application of electrical pulses. We used a surface staining procedure, with the potential sensitive dye di-4-ANEPPS, throughout our experiments which limited the depth of contribution to the optical signal to less than 40 μm. Our results gave clear evidence, that the structural inhomogeneities themselves, in regions within about a space constant (<1 mm), were able, during the application of an electrical pulse, to cause strong membrane polarizations. These polarizations, occurring far from electrodes, were sufficient to trigger local electrical activities. Our findings strongly support hypotheses, which assume, that the tissue structure - especially in regions far from electrodes or from the surface of the heart - play an important role in the defibrillation process.