PROPAGATING CALCIUM WAVES INITIATED BY LOCAL CAFFEINE APPLICATION IN RAT VENTRICULAR MYOCYTES

1. Caffeine was applied locally to one region of a resting cell via an extracellular pipette while simultaneously imaging the concentrations of intracellular calcium ([Ca2+](i)) and intracellular caffeine ([caf feine](i)). 2. Local application of caffeine produced a rise of [caffe ine](i) which was confined to the region of the cell near the pipette. There was also a local increase of [Ca2+](i) which then, in most rest ing cells, propagated along the cell as a linear Ca2+ wave. The initia l magnitude of the rise of [Ca2+](i) was greater than that of the elec trically stimulated Ca2+ transient. 3. As the wave of increase of [Ca2 +](i) propagated along the cell it decreased in both amplitude and vel ocity in cells that had not been treated to elevate the cellular Ca2load. 4. In some cells the caffeine response did not propagate signifi cantly. In these cases an increase of the cellular Ca2+ load enabled c affeine-induced Ca2+ wave propagation along the entire cell length wit hout significant decay in amplitude and velocity. 5. Previous work has shown that an electrically evoked local systolic Ca2+ transient does not propagate. The fact that the caffeine-evoked response does propaga te and the correlation between decay of amplitude and velocity suggest that the transient has to be a certain size before it can propagate. It is suggested that one of the factors which favour propagation of wa ves under conditions of elevated sarcoplasmic reticulum Ca2+ content i s the increased release of Ca2+.