Effects of anoxia on intracellular free Ca2+ in isolated cardiomyocytes from turtles.
One of the most important negative consequences of hypoxic stress in the mammalian myocardium is a breakdown in intracellular calcium homeostasis. This study examines the effects of anoxic stress on intracellular calcium regulation in isolated ventricular myocytes from a hypoxia tolerant vertebrate, the western painted turtle (Chrysemys picta bellii). Isolated calcium tolerant cardiomyocytes from turtle hearts were mounted on a glass cover slip that formed the bottom of a sealed, Plexiglas perfusion chamber. Free [Ca2+]i (determined by FURA2 fluorescence) in isolated turtle cardiomyocytes averaged 31.7 +/- 3.2 nM after 30 min of normoxic perfusion (20 degrees C, pHc = 7.77). This value is on the low end of the published range for mammalian cardiomyocytes. Perfusion with anoxic Ringer equilibrated with 3% CO2, resulted in a significant increase in free [Ca2+]i to 941 +/- 494.6 nM after 60 min. Increasing the CO2 in the perfusion solution to 5% or 6% blunted this rise (peak levels after 60 min of anoxia were 420.5 +/- 176.0 nM and 393.8 +/- 132.8 nM, respectively). A further increase to 8% CO2 increased the maximal value for free [Ca2+]i to 610.9 +/- 297.5 nM. In eight cells from the 5% CO2 protocol in which [Ca2+]i was monitored during recovery, reperfusion with normoxic Ringer rapidly lowered intracellular calcium to 92.8 +/- 9.7 nM within 15 min. Anoxia at relatively high extracellular (and hence intracellular) pH results in an increase in free [Ca2+]i comparable in magnitude and time course to that seen in some mammalian cardiomyocyte preparations. Perfusion of anoxic myocytes with Ringer equilibrated with either 5% or 6% CO2 blunted this increase in intracellular calcium, possibly an example of the pH paradox effect. A more severe combination of respiratory acidosis and anoxia (8% CO2) removed this protective effect.
Wasser
J S
JS
Max-Planck Institute for Experimental Medicine, Department of Physiology, Göttingen, Germany. jwasser@vetmed.tamu.edu
Heisler
N
N
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D014426:Turtles / Q000378:metabolism*
D005456:Fluorescent Dyes; D002118:Calcium; D016257:Fura-2