Characterization of membrane calcium channels in nonpregnant and pregnant human uterus

The binding properties of the calcium channel inhibitor [3H]-nitrendipine to membrane fragments prepared from nonpregnant and pregnant human myometrium were investigated. Specific binding sites with high affinity and low capacity were identified in both pregnant and nonpregnant myometrium. Whereas there was no significant difference in the concentration of binding sites in the two types of myometria, the Kd value for binding in pregnant myometrium was lower than that in nonpregnant myometrium (p less than 0.05). Although dihydropyridines effectively competed for [3H]-nitrendipine-binding sites, verapamil was a poor competitor. This was true for both the pregnant and nonpregnant myometrium. The inhibition of nitrendipine binding by dihydropyridines and also verapamil was significantly greater in pregnant than in nonpregnant myometrium. These data suggest that dihydropyridine-type calcium channel inhibitors might provide a useful alternative for treating premature labor.