METABOLIC EFFECTS AND CELLULAR-VOLUME RESPONSES INDUCED BY NORADRENALINE IN NUCLEATED ERYTHROCYTES

The mechanism of adrenergic swelling, cAMP accumulation and associated Na+ and K+ concentration changes was investigated in amphibian Rana r idibunda erythrocytes. The addition of noradrenaline to an isotonic su spension of red cells of frog Rana ridibunda in the presence of the ph osphodiesterase inhibitor isobutyryl-methylxanthine (IBMX), induced a significant increase of the cell volume. Forskolin treatment showed an alogous results. The removal of the Na+ from the incubation medium, in hibited the volume changes caused by either noradrenaline or forskolin . Under the same conditions a more than two-fold increase of lactate f ormation, 260% increase of glucose consumption and accumulation of cAM P were found. These effects are specific and rapid. The peak of lactat e production at 7.5 min was followed by a slow further decrease, where as cAMP reached a plateau after 15 min. The increased glycolytic rate is probably the consequence of an activation of phosphofructokinase by cAMP. When the red cells were incubated in the presence of either nor adrenaline or the cAMP analog, dibutyryl-cAMP the intracellular concen tration of Na+ was significantly increased by the first 7.5 min of inc ubation compared with the initial values. Both the adrenergic activati on and dibutyryl-cAMP treatment induced an intracellular decrease in t he K+ content by 15%. In the presence of amiloride the Na+ and the Kcontent of erythrocytes remained unaltered. Cellular swelling may be a prerequisitive for activation of Na+ and K+ movements. These findings suggest a regulatory role of cAMP in the energy metabolism of Rana ri dibunda erythrocytes. In addition, the adrenergic responses were rapid and specific to alpha(1) and beta-antagonists. (C) 1997 Wiley-Liss, I nc.