Ca super(2) super(+) release from the sarcoplasmic reticulum activated by the low affinity Ca super(2) super(+) chelator TPEN in ventricular myocytes

• Published in: Cell calcium (Edinburgh) Vol. 41; no. 2; pp. 187 - 194
• Main Authors: Jung, C, Zima, A V, Szentesi, P, Jona, I, Blatter, LA, Niggli, E
• Format: Journal Article
• Language: English
• Published: 01.02.2007
• ISSN: 0143-4160
• DOI: 10.1016/j.ceca.2006.06.009

The Ca super(2) super(+) content of the sarcoplasmic reticulum (SR) of cardiac myocytes is thought to play a role in the regulation and termination of SR Ca super(2) super(+) release through the ryanodine receptors (RyRs). Experimentally altering the amount of Ca super(2) super(+) within the SR with the membrane-permeant low affinity Ca super(2) super(+) chelator TPEN could improve our understanding of the mechanism(s) by which SR Ca super(2) super(+) content and SR Ca super(2) super(+) depletion can influence Ca super(2) super(+) release sensitivity and termination. We applied laser-scanning confocal microscopy to examine SR Ca super(2) super(+) release in freshly isolated ventricular myocytes loaded with fluo-3, while simultaneously recording membrane currents using the whole-cell patch-clamp technique. Following application of TPEN, local spontaneous Ca super(2) super(+) releases increased in frequency and developed into cell-wide Ca super(2) super(+) waves. SR Ca super(2) super(+) load after TPEN application was found to be reduced to about 60% of control. Isolated cardiac RyRs reconstituted into lipid bilayers exhibited a two-fold increase of their open probability. At the low concentration used (20-40 mu M), TPEN did not significantly inhibit the SR-Ca super(2) super(+)-ATPase in SR vesicles. These results indicate that TPEN, traditionally used as a low affinity Ca super(2) super(+) chelator in intracellular Ca super(2) super(+) stores, may also act directly on the RyRs inducing an increase in their open probability. This in turn results in an increased Ca super(2) super(+) leak from the SR leading to its Ca super(2) super(+) depletion. Lowering of SR Ca super(2) super(+) content may be a mechanism underlying the recently reported cardioprotective and antiarrhythmic features of TPEN.