Functional expression of Ca2+ ‐mobilizing α‐thrombin receptors in mRNA‐injected Xenopus oocytes

α‐Thrombin (TH) initiates a program of intracellular events that lead to DNA replication in quiescent CCL39 Chinese hamster lung fibroblasts via membrane receptors that have yet to be characterized at a molecular level. Functional TH receptors were expressed in Xenopus laevis oocytes following injection of poly(A)+ RNA from TH‐responsive CCL39 cells; their presence was demonstrated by TH‐stimulated 45Ca2+ efflux or Ca2+dependent Cl− channel activation. In voltage clamp experiments on microinjected oocytes a Ca2+ ‐activated Cl− current was detected in response to TH (0.2–10 ). The TH response was blocked by a specific TH inhibitor, and potentiated by addition of FGF or intracellular injection of GTP‐γ‐S.