Calcium channel blockers modify jejunal uptake of D-galactose in rabbits

Calcium channel blockers modify the intestinal uptake of lipids. This study was undertaken to test the hypothesis that two different types of calcium channel blockers influence the uptake of D-galactose, a sugar absorbed by the sodium-dependent glucose transporter (SGLT1) in the intestinal brush border membrane. Nisoldipine (1 mg/kg/day) or verapamil (4 mg/kg/day) were given by mouth to New Zealand white rabbits for three weeks, and then the rates of uptake of varying concentrations (2-64 mM) of galactose were examined in an in vitro preparation of jejunum using the incorporation of 14C-labeled substrate into intact tissue segments. The maximal transport capacities (Vmax) for D-galactose were increased in animals given nisoldipine or verapamil, as compared to controls. The value of the apparent Michaelis constant Km* for D-galactose was higher with nisoldipine group and lower with verapamil, than in controls. The apparent passive permeability (Pd*) of D-galactose was estimated from the uptake of L-glucose: Pd* was lower with nisoldipine and higher with verapamil, as compared to controls. The effect of these drugs on sugar uptake is not due to differences in the animals' food intake, body weight gain, or mucosal surface area. Thus, the two different classes of calcium channel blockers, the dihydropyridine nisoldipine and the phenylalkylamine verapamil, have different effects on the K(m)* and Pd*, but not on the Vmax of D-galactose uptake.