Abstract
The expression of receptors for cholecystokinin (CCK) and other similar acting Ca2+-mobilizing hormones was studied in Xenopus laevis oocytes. Poly(A)+ RNA was prepared from pancreatic AR42J cells, which normally express receptors for CCK and bombesin and the RNA injected into oocytes. The presence of these pancreatic receptors on the oocytes was then demonstrated by hormone-induced mobilization of 45Ca2+. CCK receptors were present 1 day (maximum, 2 days) after injection of RNA and were generally proportional to the amount of poly(A)+ RNA injected (1-50 ng). Oocyte CCK receptors retained selectivity for CCK analogs (CCK8 greater than unsulfated CCK8 greater than CCK4) and were blocked by the specific CCK receptor antagonist CR 1409. When poly(A)+ RNA was subjected to size fractionation on sucrose gradients, activity-inducing CCK receptors showed a single peak centered at 3 kilobases. The generality of this oocyte system for expressing Ca2+-mobilizing hormone receptors was further shown by expression of a response to bombesin after injection of AR42J cell RNA and a response to vasopressin and angiotensin II when poly(A)+ RNA from rat liver was injected. No response to CCK was demonstrable after injection of liver RNA, demonstrating the specificity of this assay.