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(Circulation Research. 2001;89:526.)
© 2001 American Heart Association, Inc.

Cellular Biology

Effects of Cytosolic ATP on Ca²⁺ Sparks and SR Ca²⁺ Content in Permeabilized Cardiac Myocytes

Zhaokang Yang, Derek S. Steele

From the School of Biology, University of Leeds, Leeds, UK.

Correspondence to Derek S. Steele, PhD, School of Biology, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK. E-mail D.steele{at}Leeds.ac.uk

Abstract — Confocal imaging was used to study the influence of cytosolic ATP on the properties of spontaneous Ca²⁺ sparks in permeabilized ventricular myocytes. Cells were perfused with mock intracellular solutions containing fluo 3. Reducing [ATP] to <0.5 mmol/L decreased the frequency but increased the amplitude of spontaneous Ca²⁺ sparks. In the presence of 20 µmol/L ATP, the amplitude increased by 48.7±10.9%, and the frequency decreased by 77.07±3.8%, relative to control responses obtained at 5 mmol/L ATP. After exposure to a solution containing zero ATP, the frequency of Ca²⁺ sparks decreased progressively and approached zero within 90 seconds. As ATP washed out of the cell, the sarcoplasmic reticulum (SR) Ca²⁺ content increased, until reaching a maximum after 3 minutes. Subsequent introduction of adenylyl imidodiphosphate precipitated a burst of large-amplitude Ca²⁺ sparks. This was accompanied by a rapid decrease in SR Ca²⁺ content to 80% to 90% of the steady-state value obtained in the presence of 5 mmol/L ATP. Thereafter, the SR Ca²⁺ content declined much more slowly over 5 to 10 minutes. The effects of ATP withdrawal on Ca²⁺ sparks may reflect reduced occupancy of the adenine nucleotide site on the SR Ca²⁺ channel. These effects may contribute to previously reported changes in SR function during myocardial ischemia and reperfusion, in which ATP depletion and Ca²⁺ overload occur.

Key Words: ATP • sarcoplasmic reticulum • Ca²⁺ sparks

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