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Action potential duration determines sarcoplasmic reticulum Ca 2+ reloading in mammalian ventricular myocytes
Author(s) -
Bassani Rosana A.,
Altamirano Julio,
Puglisi José L.,
Bers Donald M.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.067959
Subject(s) - endoplasmic reticulum , myocyte , biophysics , chemistry , medicine , biology , biochemistry
After sarcoplasmic reticulum (SR) Ca 2+ depletion in intact ventricular myocytes, electrical activity promotes SR Ca 2+ reloading and recovery of twitch amplitude. In ferret, recovery of twitch and caffeine‐induced contracture required fewer twitches than in rabbit or rat. In rat, there was no difference in action potential duration at 90% repolarization (APD 90 ) at steady state (SS) versus at the first post‐depletion (PD) twitch. The SS APD 90 was similar in ferret and rabbit (but longer than in rat). However, compared to SS, the PD APD 90 was lengthened in ferret, but shortened in rabbit. When rabbit myocytes were subjected to AP‐clamp patterns during SR Ca 2+ reloading (ferret‐ or rabbit‐type APs), reloading was much faster using the ferret AP templates. We conclude that the faster SR Ca 2+ refilling in ferret is due to the increased Ca 2+ influx during the longer PD AP. The PD versus SS APD 90 difference was suppressed by thapsigargin in ferret (indicating Ca 2+ dependence). In rabbit, the PD AP shortening depended on the preceding diastolic interval (rather than Ca 2+ ), because rest produced the same AP shortening, and SS APD 90 increased as a function of frequency (in contrast to ferret). Transient outward current ( I to ) was larger and recovered from inactivation much faster in ferret than in rabbit. Moreover, slow I to recovery (τ∼ 3 s) in rabbit was a much larger fraction of I to . Our data and a computational model (including two I to components) suggest that in rabbit the slowly recovering I to is responsible for short post‐rest and PD APs, for the unusual frequency dependence of APD 90 , and ultimately for the slower post‐depletion SR Ca 2+ reloading.