Majumder S, Kropelin B, Dhalla N S
Division of Cardiovascular Sciences, St Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada.
Cardioscience. 1992 Jun;3(2):125-9.
To investigate the effect of an overload of intracellular Ca2+ on the adrenergic receptors, rat hearts perfused with Ca(2+)-free medium for 5 or 10 minutes were reperfused (Ca(2+)-paradox) with a medium containing 1.25 mM Ca2+. The status of beta-adrenergic and alpha-adrenergic receptors in a purified sarcolemmal preparation was studied by measuring the specific binding of [3H]dihydroalprenolol and [3H]prazosin, respectively. Reperfusion with Ca(2+)-containing medium increased the density of both beta- and alpha-adrenoceptors. While the hearts perfused with Ca(2+)-free medium for 5 minutes did not show any change in the Kd values upon reperfusion, the hearts perfused with Ca(2+)-free medium for 10 minutes showed an increase in the Kd value for beta-receptors and a decrease in the Kd value for alpha-receptors. The alterations in adrenergic receptors upon reperfusion in the hearts perfused with Ca(2+)-free medium for 5 minutes were not evident if the medium contained a low concentration of Na+ (35 mM) or was maintained at a low temperature (21 degrees C) to prevent the occurrence of an overload of intracellular Ca2+. These results suggest that an overload of intracellular Ca2+ might play an important role in changing the characteristics of adrenergic receptors in diseased hearts.
为研究细胞内钙离子过载对肾上腺素能受体的影响，将用无钙培养基灌注5或10分钟的大鼠心脏，再用含1.25 mM钙离子的培养基进行再灌注（钙反常）。通过分别测定[3H]二氢阿普洛尔和[3H]哌唑嗪的特异性结合，研究纯化肌膜制剂中β-肾上腺素能受体和α-肾上腺素能受体的状态。用含钙培养基再灌注可增加β-和α-肾上腺素能受体的密度。虽然用无钙培养基灌注5分钟的心脏再灌注时Kd值没有任何变化，但用无钙培养基灌注10分钟的心脏，β-受体的Kd值增加，α-受体的Kd值降低。如果培养基含有低浓度的钠离子（35 mM）或维持在低温（21℃）以防止细胞内钙离子过载的发生，那么用无钙培养基灌注5分钟的心脏再灌注时肾上腺素能受体的改变就不明显。这些结果表明，细胞内钙离子过载可能在改变患病心脏中肾上腺素能受体的特性方面起重要作用。
