AJP - Heart Calcium Transients and Cell-Sarcomere
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Am J Physiol Heart Circ Physiol 279: H577-H585, 2000;
0363-6135/00 $5.00
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Vol. 279, Issue 2, H577-H585, August 2000

Pi inhibits the SR Ca2+ pump and stimulates pump-mediated Ca2+ leak in rabbit cardiac myocytes

G. L. Smith1, A. M. Duncan1, P. Neary2, L. Bruce1, and F. L. Burton2

1 Institute of Biomedical and Life Sciences, Glasgow University, Glasgow G12 8QQ; and 2 Department of Medical Cardiology, Glasgow Royal Infirmary, Glasgow University, Glasgow G32 2ER, Scotland

Measurements of sarcoplasmic reticulum (SR) Ca2+ uptake were made from aliquots of dissociated permeabilized ventricular myocytes using fura 2. Equilibration with 10 mM oxalate ensured a reproducible exponential decline of [Ca2+] from 600 nM to a steady state of 100-200 nM after addition of Ca2+. In the presence of 5 µM ruthenium red, which blocks the ryanodine receptor, the time course of the decline of [Ca2+] can be modeled by a Ca2+-dependent uptake process and a fixed Ca2+ leak. Partial inhibition of the Ca2+ pump with 1 µM cyclopiazonic acid or 50 nM thapsigargin reduced the time constant for Ca2+ uptake but did not affect the SR Ca2+ leak. Addition of 10 mM inorganic phosphate (Pi) decreased the rate of Ca2+ accumulation by the SR and increased the Ca2+ leak rate. This effect was reversed on addition of 10 mM phosphocreatine. 10 mM Pi had no effect on Ca2+ leak from the SR after complete inhibition of the Ca2+ pump. In conclusion, Pi decreases the Ca2+ uptake capacity of cardiac SR via a decrease in pump rate and an increase in Ca2+ pump-dependent Ca2+ leak.

cardiac; heart; sarcoplasmic reticulum; calcium; phosphate; calcium-adenosine 5'-triphosphatase; rabbit; inorganic phosphate


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