The presence of thromboxane A2 receptors in cultured astrocytes from rabbit brain

We have previously shown that human astrocytoma cells (1321N1) express thromboxane A2 (TXA2) receptors, of which stimulation activates phosphoinositide hydrolysis (Nakahata et al., Eur. J. Pharmacol. 162 (1989) 407). In order to examine whether TXA2 receptors exist in native astrocytes or not, rabbit cultured astrocytes were used. Glial fibrillary acidic protein (GFAP)-positive astrocytes were obtained three weeks after culture of brain. [3H]ONO NT-126, a TXA2 antagonist, bound to the membranes derived from cultured rabbit astrocytes with the dissociation constant (Kd) of 0.23 nM and the maximum binding site (Bmax) of 69.5 fmol/mg protein. STA2, a stable TXA2 receptor agonist, activates phosphoinositide hydrolysis in a concentration-dependent manner, and S-145, a TXA2 antagonist, inhibited STA2-induced phosphoinositide hydrolysis. The results indicate that TXA2 receptors exist in cultured rabbit astrocytes and the activation of TXA2 receptors results in phosphoinositide hydrolysis.