VITAMIN-D STATUS MODULATES RAT COLONIC M(3)-MUSCARINIC RECEPTOR CHARACTERISTICS AND COUPLING TO GUANYLATE-CYCLASE

The present studies were conducted to determine whether [H-3]quinuclid inyl benzilate binding in rat colonic membranes and/or carbachol-media ted stimulation of particulate guanylate cyclase were altered by chang es in vitamin D status. EC,, values for the stimulation of colonic gua nylate cyclase by carbachol were found to be significantly greater in vitamin D-deficient rats compared to their D-sufficient counterparts. Concomitantly, the density of receptors (B-max) were significantly low er, and dissociation constants (K-d) were significantly higher in D-de ficient colonic membranes. In vitamin D-repleted animals, moreover, al l of these aforementioned alterations were at least partially correcte d.