Influence of pertussis toxin on parathyroid hormone stimulated cyclic AMP production and phosphate transport in opossum kidney cells.

There is evidence that guanine nucleotide-sensitive (G) proteins intervene in the activation of adenylate cyclase by parathyroid hormone (PTH). Furthermore, recent studies suggest that G proteins may be involved in the activation by PTH of phospholipase C, with subsequent elevation of diacylglycerol, inositol trisphosphate, and intracellular calcium. Since G proteins may be involved in both transduction systems postulated to mediate the actions of PTH, the present studies were performed to evaluate the influence of pertussis toxin, which prevents receptor-mediated activation of G proteins, on the effects of PTH in opossum kidney (OK) cells. In OK cell membranes, pertussis toxin catalyzed the adenosine diphosphate (ADP) ribosylation of a protein with a molecular weight of 41 kd on SDS-PAGE. Cholera toxin catalyzed the ribosylation of two proteins of molecular weight 52 and 45 kd. Pretreatment of the cells with pertussis toxin abolished the labelling of this 41 kd protein, confirming the access of the toxin into the cells and the presence of pertussis toxin-sensitive substrates. The ribosylation of the cholera toxin substrates was unaffected by pertussis toxin pretreatment of the cells. Treatment of OK cells with pertussis toxin did not change the basal levels of cyclic AMP, but increased the levels of cyclic AMP in response to bPTH 1-34 from 355 +/- 17 to 449 +/- 20 pmoles cyclic AMP per 5 minutes per culture. These results were consistent with the inactivation of an inhibitory G protein. Furthermore, PTH-stimulated cyclic AMP generation was inhibited by norepinephrine from 362 +/- 10 to 228 +/- 18 pmole cyclic AMP per 5 minutes per culture.(ABSTRACT TRUNCATED AT 250 WORDS)