Temperature dependence of Ca2+ wave properties in cardiomyocytes: implications for the mechanism of autocatalytic Ca2+ release in wave propagation.
Digital imaging microscopy of fluo-3 fluorescence was used to study the velocity and shape of intracellular Ca2+ waves in isolated rat cardiomyocytes as a function of temperature. Decreasing the temperature from 37 to 17 degrees C reduced the longitudinal wave velocity by a factor of 1.8 and remarkably slowed the decay of [Ca2+]i in the trailing flank of a wave. Using image analysis, rise times, and half-maximum decay times of local Ca2+ transients, which characterize the processes of local Ca2+ release and removal, were determined as a function of temperature. Apparent activation energies for wave front propagation, local Ca2+ release, and local Ca2+ removal were derived from Arrhenius plots and amounted to -23, -28, and -46 kJ/mol, respectively. The high activation energy of Ca2+ removal, which arises from the activity of the sarcoplasmic reticulum (SR) Ca2+ ATPase, relative to those of longitudinal wave propagation and local Ca2+ release excludes the hypothetical mechanism of regenerative "spontaneous Ca2+ release," in which Ca2+ that has been taken up from the approaching wavefront triggers Ca2+ release at a luminal site of the SR. It is consistent, however, with the hypothesis that Ca2+ wave propagation is based on Ca(2+)-induced Ca2+ release where Ca2+ triggers release on the cytosolic face of the SR.
Engel
J
J
Max Planck Institute for Biophysical Chemistry, Department of Spectroscopy, Göttingen, Germany.
Sowerby
A J
AJ
Finch
S A
SA
Fechner
M
M
Stier
A
A
D000814:Aniline Compounds; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D017136:Ion Transport; D008954:Models, Biological; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013816:Thermodynamics; D014966:Xanthenes
D000814:Aniline Compounds; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D000252:Calcium-Transporting ATPases; D002118:Calcium