Quantification of calcium release from the sarcoplasmic reticulum in rainbow trout atrial myocytes.
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.
Hove-Madsen
L
L
Dept. Cell Biology, Physiology and Immunology, Faculty of Science, Universitat Autònoma de Barcelona, Spain. Leif@cc.uab.es
Llach
A
A
Tort
L
L
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004553:Electric Conductivity; D006325:Heart Atria; D007211:Indoles / Q000494:pharmacology; D009119:Muscle Contraction / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
D002121:Calcium Channel Blockers; D007211:Indoles; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium; C000543:cyclopiazonic acid