Ca2+ release from the sarcoplasmic reticulum activated by the low affinity Ca2+ chelator TPEN in ventricular myocytes.
The Ca2+ content of the sarcoplasmic reticulum (SR) of cardiac myocytes is thought to play a role in the regulation and termination of SR Ca2+ release through the ryanodine receptors (RyRs). Experimentally altering the amount of Ca2+ within the SR with the membrane-permeant low affinity Ca2+ chelator TPEN could improve our understanding of the mechanism(s) by which SR Ca2+ content and SR Ca2+ depletion can influence Ca2+ release sensitivity and termination. We applied laser-scanning confocal microscopy to examine SR Ca2+ 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 Ca2+ releases increased in frequency and developed into cell-wide Ca2+ waves. SR Ca2+ 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 (20-40microTPEN did not significantly inhibit the SR-Ca2+-ATPase in SR vesicles. These results indicate that TPEN, traditionally used as a low affinity Ca2+ chelator in intracellular Ca2+ stores, may also act directly on the RyRs inducing an increase in their open probability. This in turn results in an increased Ca2+ leak from the SR leading to its Ca2+ depletion. Lowering of SR Ca2+ content may be a mechanism underlying the recently reported cardioprotective and antiarrhythmic features of TPEN.
Jung
C
C
Department of Physiology, University of Bern, Buehlplatz 5, 3012 Bern, Switzerland.
Zima
A V
AV
Szentesi
P
P
Jona
I
I
Blatter
L A
LA
Niggli
E
E
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005029:Ethylenediamines / Q000494:pharmacology*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D032342:Muscle Cells / Q000187:drug effects / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D000099211:Phospholamban
D002110:Caffeine; D002118:Calcium; D002135:Calcium-Binding Proteins; D005029:Ethylenediamines; D019837:Ryanodine Receptor Calcium Release Channel; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine