Calcium-induced contraction and contractile protein of gallbladder smooth muscle after high-cholesterol feeding of prairie dogs.

Feeding a high-cholesterol diet to prairie dogs causes a reduction in contractile responses of gallbladder smooth muscle from these animals. In this study, the influence of cholesterol feeding on the contractile response to calcium and on the concentration of the contractile proteins actin and myosin was determined. Strips of gallbladder smooth muscle, at their optimal length for tension development, were stimulated maximally with carbachol. Then the muscle cell membranes were made permeable and strips were exposed to a maximally effective concentration of calcium. Strips from cholesterol fed animals developed less stress than those from control animals under all conditions. The concentration of actin and myosin was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There were no differences in the concentrations of either protein between the cholesterol-fed and control animals. Our results indicate that the decreased contractile response seen in muscle from cholesterol-fed animals is not due to alterations in membrane excitation, excitation-contraction coupling, or in total contractile proteins.