Abstract
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 allows realistically small values for SR calcium leak
fluxes to be used. Total cytosolic calcium was calculated from the
latter part of Ca(i) decline using rate constants for cellular
calcium buffers. Intra-SR calcium buffering characteristics were
also deduced. We found that the net SR calcium pump 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
first time in intact myocytes both forward and reverse SR calcium
pump kinetics as well as intra-SR calcium buffering and SR calcium
leak. We conclude that the reverse flux through the SR calcium pump
is an important factor in comprehensive understanding of dynamic
SR calcium fluxes.
- 10620296
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