DESENSITIZATION OF PROSTACYCLIN RECEPTORS IN A NEURONAL HYBRID CELL LINE

1 Prostacyclin and its stable analogue, carbacyclin, bind competitively to a single population of receptors, and activate adenylate cyclase of the NCB‐20 neuronal somatic cell hybrid ( K act = 40.1 nM and 96.1 nM respectively). 2 Culture of NCB‐20 cells in the presence of 1 μ m carbacyclin for 4 to 16 h results in a progressive decrease in the prostacyclin‐dependent activation of adenylate cyclase in cell homogenates with an increase at 16 h of the K act from 64.1 n m to 174.0 n m and decrease in the maximum adenylate cyclase activation from 41.2 to 15.1 pmol cyclic AMP min −1 mg −1 protein. 3 The prediction that the apparent decrease in affinity in the prostacyclin‐dependent activation of adenylate cyclase was secondary to a reduction in receptor numbers was tested directly by measuring binding of [ 3 H]‐prostacyclin to membranes of cells exposed to carbacyclin for 16 h. This showed an actual decrease in affinity of the prostacyclin‐receptor interaction, as well as a decrease in the total receptor numbers. Thus prolonged exposure of NCB‐20 cells to carbacyclin caused reductions in both receptor numbers and affinity, reflected by measurements both of binding and adenylate cyclase activation.