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.
|Original language||English (US)|
|Number of pages||12|
|State||Published - 2000|
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