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