Quantification of calcium release from the sarcoplasmic reticulum in rainbow trout atrial myocytes

Pflugers Arch. 1999 Sep;438(4):545-52. doi: 10.1007/s004249900082.


Using the whole-cell configuration of the patch-clamp technique, we quantified calcium release from the sarcoplasmic reticulum (SR) elicited by short depolarization pulses before and after clearance of the SR Ca2+ content with 10 mM caffeine (CAF). With a loaded SR, the first detectable contraction occurred with a pulse duration of 5 ms. CAF exposure increased this pulse duration to 85 ms and slowed the inactivation of the Ca2+ current (ICa). Repolarization of the cell to -80 mV after a short depolarization elicited a tail current that was attenuated markedly after CAF exposure. The difference between the charge carried by the tail currents obtained before and after CAF exposure was taken as a measure of the Ca2+ released from the SR. SR Ca2+ release increased with increasing SR Ca2+ load over the range of loads examined. In contrast, SR Ca2+ release reached a maximum when the duration of the preceding depolarization exceeded 10 ms. Maximal Ca2+ release was 1.64 amol/pF or 62 microM and elicited a contraction that was 40 +/- 6% of the amplitude of a normal contraction. This release could account for 48 +/- 10% of the total Ca2+ required to activate contraction but only a few percent of the CAF-releasable Ca2+. Thus, contrary to the general view of excitation-contraction coupling in lower vertebrates, SR Ca2+ release in trout atrial myocytes may account for up to 50% of the total Ca2+ transient at room temperature.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Calcium / pharmacology
  • Calcium / physiology
  • Calcium Channel Blockers / pharmacology
  • Electric Conductivity
  • Heart Atria
  • Indoles / pharmacology
  • Muscle Contraction / physiology
  • Myocardium / cytology
  • Myocardium / metabolism*
  • Oncorhynchus mykiss / metabolism*
  • Ryanodine / pharmacology
  • Sarcoplasmic Reticulum / drug effects
  • Sarcoplasmic Reticulum / metabolism*


  • Calcium Channel Blockers
  • Indoles
  • Ryanodine
  • Caffeine
  • Calcium
  • cyclopiazonic acid