DIVERSITY OF EARLY AFTERDEPOLARIZATIONS IN GUINEA-PIG MYOCYTES - SPATIAL CHARACTERISTICS OF INTRACELLULAR CA2+ CONCENTRATION

We classified early afterdepolarizations (EADs) into subgroups accordi ng to the spatial features of the intracellular Ca2+ concentration ([C a2+](i)). Myocytes were enzymatically isolated from guinea pig ventric les. When fura-2 salt was applied through a whole cell patch pipette a fter the formation of a gigaohm seal, the membrane potential was measu red using the current, clamp technique. When myocytes were loaded with fura-2 AM, the membrane potential was recorded with a conventional mi croelectrode technique. Spatio-temporal changes in fura-2 fluorescence and cell length were recorded simultaneously, using a digital TV syst em. EADs were induced after superfusion with potassium-free Tyrode sol ution. Irrespective of the fura-2 loading procedure, EADs could be cla ssified into those with spatially synchronous fluorescence changes (n = 26 from eight hearts) and those with heterogeneous changes (n = 20 f rom three hearts). EADs with synchronous features took off from a high er membrane potential (greater than or equal to-34mV) than EADs with h eterogeneous features (less than or equal to-57 mV). These results sug gest that EADs have at least two constituents.