Gq/11 communicates with thromboxane A2 receptors in human astrocytoma cells, rabbit astrocytes and human platelets.

Western blot analysis was performed to clarify the presence of trimeric G protein subfamily in membranes derived from human astrocytoma cells (1321N1), cultured rabbit astrocytes and human platelets, using G protein antisera GS alpha, Gi alpha, Gq/11 alpha, and G beta were found to exist in membranes derived from human astrocytoma cells and rabbit astrocytes as well as human platelets. However, only small amount of G(o) alpha was detected in any membranes. Gq/11 alpha was expressed much more in human platelets than in human astrocytoma cells or rabbit astrocytes. 9,11-Epithio-11,12-methanothromboxane A2 (STA2), a stable analogue of thromboxane A2 (TXA2), activated GTPase in membranes derived from human astrocytoma cells, rabbit astrocytes and human platelets with different potencies. STA2-induced GTPase activation in human platelet membranes was partly inhibited by treatment with QL antibody at 0 degrees C for 90 min. Furthermore, STA2-induced GTPase activation in membranes derived from human astrocytoma cells and rabbit astrocytes were potently inhibited by treatment with QL antibody. The results obtained indicate that TXA2 receptors in human astrocytoma cells and rabbit astrocytes communicate with Gq/11 as well as in human platelets.