| CHRONIC EXPOSURE TO DIFFERENT AMBIENT TEMPERATURES AFFECTS b-AR PROFILE AND HEART RESPONSIVENESS TO ISOPROTERENOL AND CALCIUM |
YEHUDA ARIELI A1, PAVEL KASPLER A2, MICHAL HOROWITZ A2
A1 Department of Animal and Cell Biology, Alexander Silberman Institute of Life, Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel and the Department of Physiology, Hadassah School of Dental Medicine and Medicine, The Hebrew University of Jerusalem, P.O. Box 12272, Jerusalem 91120, Israel
A2 Department of Physiology, Hadassah School of Dental Medicine and Medicine, The Hebrew University of Jerusalem, P.O. Box 12272, Jerusalem 91120, Israel
The purpose of this investigation was to study the effect of thermal acclimation on the myocardium of rock pigeons. We determined the density and affinity of the b -adrenergic receptors in the left ventricle of cold-, heat-, and normothermic-acclimated pigeons by radioligand binding techniques. The mechanical performance of the left ventricle of the heart subjected to either isoproterenol or Ca2+ loading was measured using the Langendorff perfusion system. Heat- and cold-acclimated hearts demonstrated a significant downregulation of b - and b2 -adrenoreceptor density accompanied by an increase in their affinity when compared with normothermic-acclimated hearts. In agreement with these results, isoproterenol improved cardiac performance in cold- and heat-acclimated hearts. We also found that the heat-acclimated hearts were capable of functioning successfully when exposed to high Ca2+ loads, whereas cold-acclimated hearts were significantly less tolerant of Ca2+ loads and less efficient. Thermal acclimation induces cellular alterations in the pigeon heart, thus enabling better coping with hemodynamic and calcium loads, both resulting from thermal stress.
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