Mechanism of intracellular calcium homeostasis in heat-exposed cardiomyocytes of rats

The activity of Ca(2+)-ATPase and calcium content were measured in sarcoplasmic reticulum (SR) and mitochrondria of myocardium from 40 adult female Wistar rats after exposure to 37 degrees C, 39 degrees C, 41 degrees C and 43 degrees C for 40 min respectively in vitro. The 45Ca uptake, intracellular free Ca2+ concentration (Ca2+]i) and the relatively active calmodulin content were also observed in cultured cardiomyocytes from 120 neonatal Wistar rats under the same condition of heat exposure. The results showed that (1) the activity of Ca(2+)-ATPase of SR and mitochrondria of myocardium decreased after heat exposure, (2) the calcium content of SR and mitochrondria also showed a tendency of decrease with increase of exposure temperature, (3) the 45Ca uptake and mean Ca2+]i increased, whereas the calmodulin content decreased. It is suggested that disturbances of intracellular calcium homeostasis may be responsible for cardiac functional disorder after heat exposure.