Identification of a single (FP) receptor associated with prostanoid-induced Ca 2+ signals in swiss 3T3 cells

Abstract

Thus far, the prostanoid FP-receptor has been characterized only on the basis of agonist studies. It is currently classified as a receptor having particular sensitivity to prostaglandin F 2α (PGF 2α) but with the ability to recognize prostaglandins D 2 and E 2 (PGD 2 and PGE 2). We have re-examined this concept by studying second messenger Ca 2+ signals to PGF 2α, PGD 2 and PGE 2, and performing radioligand binding studies in Swiss 3T3 cells. The same rank order of potency was obtained for both the Ca 2+ transient signal and competition for PGF 2α binding sites. The potency rank order, PGF 2 α >PGD 2>PGE 2, was identical to that obtained from functional studies in isolated tissues, such as the cat iris. Additional support for the concept that PGF 2α, PGD 2, and PGE 2 interact with a single receptor to elicit a Ca 2+ signal was provided by successive addition studies. Thus, cells pretreated with a supramaximal concentration of PGF 2α exhibited little or no response to subsequent administration of PGD 2 or PGE 2. Likewise, cells pretreated with a large concentration PGD 2 or PGE 2 exhibited minimal responsiveness to successive addition of the corresponding alternative prostaglandins. Pretreatment with a maximally effective concentration of PGF 2α, PGD 2, or PGE 2 rendered the cells refractory to the FP-receptor selective agonist fluprostenol, which further supports the hypothesis that Ca 2+ transient signals in response to prostanoids in Swiss 3T3 cells are mediated by the FP-receptor. The Ca 2+ transient responses to PGF 2α, PGD 2, and PGE 2 also exhibited a similar modest reduction when extracellular Ca 2+ was removed. Finally, the DP-receptor antagonist BW A868C did not block the Ca 2+ transient response to PGD 2, indicating an absence of DP-receptor involvement. Moreover, Ca 2+ responses to the thromboxane A 2 mimetic U-46619 were unaffected by the TP-antagonist BM 13505, which indicates no involvement of the TP-receptor. These results support the contention that the FP-receptor has particular sensitivity to PGF 2α but will also recognize PGD 2 and PGE 2.