IN-VITRO EFFECT OF HYDROCORTISONE ON THE CALCIUM DISTRIBUTION IN RAT THYMOCYTES

Chlorotetracycline (CTC) was used as a fluorescence indicator for inve stigation of the intracellular membrane-bound Ca2+ redistribution in t he hydrocortison (HC)-treated rat thymocytes. The effect of KC (0.1-1 mu M) on the thymocytes incubated in Ca2+-containing media for 60-120 min increased 1,5-fold the quantity of the membrane-bound Ca2+ in the plasma membrane. When thymocytes were incubated in Ca2+-free media, no HC-induced changes in the Ca2+ pool in the plasma membrane were found . In the presence of inhibitors of respiration and oxidative phosphory lation, the CTC fluorescence intensity in the HC-treated cells decreas ed to a greater extent than in the control, thereby indicating an incr ease in the mitochondrial Ca2+ pool. Using inhibitors of endoplasmic r eticulum Ca2+-ATPase (vanadate, BHQ), HC was shown to decrease the non mitochondrial Ca2+ pool. Calmodulin blockers (triphtasyne and R24) sli ghtly decreased the CTC fluorescence intensity in the HC-treated cells as compared to the control. HC was found to inhibit the calmodulin-me diated Ca2+ accumulation in the thymocyte membrane. Based on the exper iments using AlF4-, we concluded that HC stimulates the activity of G- proteins by the receptor-mediated mechanism. A possible role of the ob served Ca2+ redistribution between the thymocyte intracellular compart ments, in particular, between mitochondria and endoplasmic reticulum, was discussed.