Me. Diaz et al., The effects of exogenous calcium buffers on the systolic calcium transientin rat ventricular myocytes, BIOPHYS J, 80(4), 2001, pp. 1915-1925
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.