NUCLEOTIDES REGULATE THE BINDING-AFFINITY OF THE RECOMBINANT TYPE-A CHOLECYSTOKININ RECEPTOR IN CHO K1 CELLS

Cholecystokinin (CCK) receptors on rat pancreatic acinar cells display two binding affinity states in the presence of adeninine and guanine triphosphates with the effect of ATP mediated by the enzyme nucleoside diphosphate kinase. To determine whether this behavior was intrinsic to a single receptor protein we studied the binding affinity of CHO ce lls stably transfected with a cloned rat CCK, receptor. I-125-CCK bind ing to intact cells at 37 degrees C revealed two affinity states for C CK of K-d values 20 pM and 2.4 nM. Membranes prepared from these cells displayed a single affinity state for CCK but two affinity states cou ld be restored in the presence of GTP[gamma S], ATP and ATP[gamma S] b ut not AMP-PCP. ATP and TTP[gamma S] but not AMP-PCP were substrates f or nucleoside diphosphate kinase present in CHO cell membranes and tra nsferred their terminal phosphate to GDP. These findings indicate that the interconvertible affinity states of the CCK receptor are inherent in a single receptor protein and that nucleoside diphosphate kinase m ediates the effect of ATP to regulate these two affinity states