Effects of volatile anesthetics on light-induced proton uptake of rhodopsin in bovine rod outer segment disk membrane.

Abstract

The effects of volatile anesthetics upon the function of bovine rhodopsin were estimated from the measurements of light-induced proton uptake. The light-induced pH changes were measured at both 20 degrees C and 37 degrees C with suspensions to which volatile anesthetics were added in the liquid form. Each anesthetic depressed the light-induced proton uptake concentration-dependently. The anesthetic-induced depression was greater at 37 degrees C than at 20 degrees C. For each anesthetic the concentration needed to depress the proton uptake by 10% was roughly identical to that used clinically. Anesthetics also were added to the suspensions in the gaseous form with air. The light-induced proton uptake was decreased in proportion to the partial pressure of the anesthetic. The partial pressures of halothane and methoxyflurane that depressed the proton uptake by 10% at 37 degrees C were 2.0 x 10(-7) and 1.1 x 10(-2) atm., respectively. From these facts it is suggested that volatile anesthetics affect the light-induced conformational changes of rhodopsin molecule during the metarhodopsin I to metarhodopsin II transition and cause inhibition of the light-induced proton uptake of rhodopsin in the rod outer segment disk membrane.