Effects of Volatile Anesthetics on Light-induced Proton Uptake of Rhodopsin in Bovine Rod Outer Segment Disk Membrane

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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.degree. and 37.degree. 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.degree. than at 20.degree. 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.degree. C were 2.0 .times. 10-2 and 1.1 .times. 10-2 atm., respectively. 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 disc membrane.