Binary combinations of propofol and barbiturates on human alpha(1) glycine receptors expressed in Xenopus oocytes.

To test whether there is a common site of action for intravenous anaesthetics at the glycine receptor, the effects of binary combinations of thiopentone, pentobarbitone, methohexitone, and propofol have been tested on human alpha(1) glycine receptors expressed in Xenopus laevis oocytes using two-electrode voltage-clamp techniques. Thiopentone (5-40 microM), pentobarbitone (25-400 microM) and propofol (2-100 microM) (but not methohexitone), potentiated the glycine-induced (50 microM) current in a dose-dependent manner, with the maximum potentiation observed to be 218%, 400%, and 576%, respectively. In binary combination with thiopentone, pentobarbitone or propofol, methohexitone reduced potentiation compared to that by the individual anesthetics to 190%, 260% and 460%, respectively. Combination of thiopentone and pentobarbitone (50 microM) increased potentiation, compared to that by thiopentone alone. Binary combinations of propofol with either thiopentone or pentobarbitone showed more potentiation, compared to that observed with the individual anesthetics. Our results indicate that thiopentone, pentobarbitone and propofol all act as positive allosteric modulators at the alpha(1) glycine receptor. In contrast, methohexitone has no action alone but acts as a competitive antagonist to thiopentone, pentobarbitone and propofol. We suggest that, on the basis of these results, these four intravenous anaesthetics share a common site of action at the glycine receptor.