Modulation of dihydropyridine-sensitive gastric mucosal calcium channels by GM1-ganglioside

1. A dihydropyridine-sensitive calcium channel complex was solubilized from gastric mucosal cell membranes and purified by affinity chromatography on wheat germ agglutinin. 2. The calcium channel complex labeled with [3H]PN200-110, when reconstituted into phosphatidylcholine vesicles, exhibited active 45Ca2+ uptake into intravesicular space as evidenced by La3+ displacement and osmolarity studies. The channel complex responded in a dose-dependent manner to dihydropyridine calcium antagonist, PN200-110, which at 0.5 microM exerted maximal inhibitory effect of 66% in 45Ca2+ uptake. 3. The uptake of 45Ca2+ into vesicle-reconstituted gastric mucosal calcium channel complex was inhibited by GM1-ganglioside. Maximum inhibitory effect was achieved at 10-15 nM GM1, at which point a 74% decrease in 45Ca2+ uptake occurred. Furthermore, GM1 also inhibited dihydropyridine binding to gastric mucosal membranes, indicating the extracellular orientation of calcium channel domains for GM1. 4. The ability of GM1 to modulate the intracellular calcium levels may be an important feature in gastric mucosal protection by this ganglioside.