Calcium homeostasis in cardiomyocytes isolated from heat-shocked rats.
The cellular mechanism of heat shock-mediated cardioprotection is still under debate. Because heat pretreatment negatively affects the normoxic left ventricular contractile performance in vitro when the extracellular Ca2+ concentration ([Ca2+]o) is relatively low (0.65-1.25 mM), the intracellular Ca2+ homeostasis was studied in more detail in cardiomyocytes isolated from adult rats 24 h after heat stress (42 degrees C for 15 min) or anesthesia (control). Sensitivity to Ca2+ overload was assessed by exposure to veratridine (quiescent cells) or to [Ca2+]o ranging from 0.125 to 20 mM in quiescent and paced cardiomyocytes. The fraction of irreversibly hypercontracted cells was not different between groups. The fura-2 fluorescence ratio (I340/I380), which was used as a measure for cytoplasmic Ca2+ concentration ([Ca2+]i) in quiescent cells after exposure to [Ca2+]o (0.5-10 mM), was also not different between groups. Myofilament Ca2+ sensitivity was assessed in paced (0.5 Hz) cells by simultaneous measurement of [Ca2+]i transients and cell shortening. At stepwise increases of [Ca2+]o from 1 to 10 mM, these parameters were comparable between groups. The diastolic cell length shortened progressively and equally in both groups after increasing [Ca2+]o. However, within 2 min of return from 10 to 1 mM [Ca2+]o, cells from heat-shocked rats retained the same length, whereas cells from control rats contracted further (P = 0.05). These data suggest that heat stress improves relaxation after challenge with high [Ca2+]o.
Cornelussen
R N
RN
Department of Physiology, Institute Maastricht, University of Limburg, The Netherlands.
Ver Donck
L
L
Verellen
G
G
Borgers
M
M
van der Vusse
G J
GJ
Reneman
R S
RS
Snoeckx
L H
LH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002469:Cell Separation; D003593:Cytoplasm / Q000378:metabolism; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D016257:Fura-2; D006706:Homeostasis; D006358:Hot Temperature; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D012769:Shock / Q000378:metabolism* / Q000473:pathology; D014701:Veratridine / Q000494:pharmacology
D014701:Veratridine; D002118:Calcium; D016257:Fura-2