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ANESTHETIC PHARMACOLOGY

The Effects of Hexanol on G_i Subunits of Heterotrimeric G Proteins

John Streiff, PhD^*, David O. Warner, MD^*, Elena Klimtchuk, PhD, William J. Perkins, MD^*, Kristofer Jones, BS, and Keith A. Jones, MD^*

Departments of *Anesthesiology and Physiology and Biophysics, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Address correspondence and reprint requests to David O. Warner, MD, Mayo Clinic and Foundation, 200 First St. S.W., Rochester, MN 55905. Address e-mail to warner.david{at}mayo.edu

Alcohols and other anesthetics interfere with the function of a variety of systems regulated by guanosine triphosphate (GTP)-binding proteins (G proteins). We examined the effect of hexanol on the activity of the subunit (G_i1) of heterotrimeric G proteins. The GTP hydrolysis activity of recombinant G_i1 was 0.029 mole Pi · mole G_i1^-1 · min^-1 and was inhibited by hexanol at concentrations larger than 10 mM, with a 50% inhibitory concentration of 22 mM. Circular dichroism spectroscopy revealed that hexanol decreased the denaturation temperature of G_i1 from 47.2°C to 42.5°C without altering its secondary structure at 10°C. Hexanol (30 mM) reduced the amount of monomeric G_i1 in solution measured by size-exclusion chromatography, indicating that hexanol caused protein aggregation. However, the rate of GTPS binding to G_i immunoprecipitated from airway smooth muscle membranes was not affected by 30 mM hexanol. Excluding the apparent inhibition of recombinant G_i1 resulting from aggregation-induced artifact, we found no evidence that the hexanol-induced inhibition of receptor-activated G_i-coupled pathways in intact airway smooth muscle resulted from direct inhibition of the intrinsic rate of [³⁵S]GTPS binding to G_i.

IMPLICATIONS: Although the subunit of heterotrimeric G proteins is a potential target of anesthetics, we found no evidence that hexanol affects the ability of the G_i subunit to bind or hydrolyze guanosine triphosphate, either in purified subunits or in subunits derived from smooth muscle cell membranes. This finding implies that this is not a mechanism by which hexanol interferes with receptor-G protein function.

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