| Abstract: | Purified rat tumour Leydig cells were pretreated with or without lutropin (1 h at 32 degrees C). The plasma membranes were then isolated and the adenylate cyclase activity measured in the presence of freshly prepared or heat-inactivated (1 h at 60 degrees C) human erythrocyte membranes. In plasma membranes from control cells in the presence of heat-inactivated human erythrocyte membranes both guanosine 5'-beta, gamma-imido]triphosphate (pNH]ppG) plus lutropin and NaF caused a 45--50-fold increase in cyclic AMP production over 30 min compared with 12--13 fold pNHppG and 2--3-fold with lutropin alone. In plasma membranes isolated from lutropin-pretreated cells the NaF- and the pNH]ppG-stimulated cyclic AMP production rates were unchanged, but no effect of lutropin could be demonstrated with or without added pNH]ppG. However, after mixing lutropin-desensitized Leydig tumour-cell plasma membranes with freshly prepared human erythrocyte plasma membranes, the adenylate cyclase activity in the presence of lutropin, pNH]ppG, lutropin plus pNH]ppG and NaF were similar to those of control cell plasma membranes treated in the same manner. The possible mechanisms of this reversal of lutropin-induced desensitization by human erythrocytes are discussed. |
