Generation of Myocyte Agonal Ca Waves and Contraction Bands in Perfused Rat Hearts Following Irreversible Membrane Permeabilisation

Although irreversible cardiomyocyte injury provokes intracellular Ca ([Ca]) overload, the underlying dynamics of this response and its effects on cellular morphology remain unknown. We therefore visualised rapid-scanning confocal fluo4-[Ca] dynamics and morphology of cardiomyocytes in Langendorff-perfused rat hearts following saponin-membrane permeabilisation. Our data demonstrate that 0.4% saponin-treated myocytes immediately exhibited high-frequency Ca waves (131.3 waves/min/cell) with asynchronous, oscillatory contractions having a mean propagation velocity of 117.8 μm/s. These waves slowly decreased in frequency, developed a prolonged decay phase, and disappeared in 10 min resulting in high-static, fluo4-fluorescence intensity. The myocytes showing these waves displayed contraction bands, i.e., band-like actin-fibre aggregates with disruption of sarcomeric α-actinin. The contraction bands were not attenuated by the abolition of Ca waves under pretreatment with ryanodine plus thapsigargin, but were partially attenuated by the calpain inhibitor MDL28170, while mechanical arrest of the myocytes by 2,3-butanedione monoxime completely attenuated contraction-band formation. The depletion of adenosine 5'-triphosphate by the mitochondrial electron uncoupler carbonyl cyanide 4-trifluoromethoxy phenylhydrazone also attenuated Ca waves and contraction bands. Overall, saponin-induced myocyte [Ca] overload provokes agonal Ca waves and contraction bands. Contraction bands are not the direct consequence of the waves but are caused by cross-bridge interactions of the myocytes under calpain-mediated proteolysis.