Tr. Shannon et al., Reverse mode of the sarcoplasmic reticulum calcium pump and load-dependentcytosolic calcium decline in voltage-clamped cardiac ventricular myocytes, BIOPHYS J, 78(1), 2000, pp. 322-333
We have characterized [Ca](i) decline in voltage-clamped rabbit ventricular
myocytes with progressive increases in sarcoplasmic reticulum (SR) calcium
load, "Backflux" through the SR calcium pump is a critical feature which a
llows realistically small values for SR calcium leak fluxes to be used, Tot
al cytosolic calcium was calculated from the latter part of [Ca](i) decline
using rate constants for cellular calcium buffers, Intra-SR calcium buffer
ing characteristics were also deduced, We found that the net SR calcium pum
p flux and rate of [Ca](i) decline decreased as the SR free [Ca] rose, with
pump parameters held constant. We have therefore characterized for the fir
st time in intact myocytes both forward and reverse SR calcium pump kinetic
s as well as intra-SR calcium buffering and SR calcium leak. We conclude th
at the reverse flux through the SR calcium pump is an important factor in c
omprehensive understanding of dynamic SR calcium fluxes.