The effects of exogenous calcium buffers on the systolic calcium transientin rat ventricular myocytes

The aim of this work was to characterize the effects that two commonly used "caged" calcium buffers (NP-EGTA and nitr-5) have on the amplitude and tim e course of decay of the calcium transient. We made quantitative measuremen ts of both free and total calcium using the measured buffering properties o f the cell. Intracellular calcium concentration ([Ca2+](i)) was measured wi th fluo-3 in rat ventricular myocytes. Incorporation of the buffer NP-EGTA decreased both the amplitude and rate of decay of the caffeine response. Th e slowing could be quantitatively accounted for by the measured increased b uffering. These effects were removed by photolysis of NP-EGTA. Similar resu lts were obtained with nitr-5 except that the effects were not completely r emoved by photolysis. This was shown to be due to the persistence of a comp onent of the increased buffering after photolysis. Both buffers decreased t he amplitude of the systolic calcium transient. However, although nitr-5 pr oduced a simple slowing of the decay, NP-EGTA resulted in an initial rapid phase of decay, This rapid phase of decay is attributed to calcium binding to NP-EGTA. This work represents the first quantitative analysis of the eff ects that extra buffering by a fast and a slow calcium chelator may have on the calcium transient.