EFFECTS OF CALCIUM IONS AND MAGNESIUM IONS ON 5-HYDROXYTRYPTAMINE-RECEPTOR INTERACTION

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Abstract
Which divalent cations, Ca or Mg ions in physiological solution, are necessary for the [rat uterus] 5-HT[5-hydroxytryptamine]-receptor to interact with 5-HT was studied. Phenoxybenzamine was used to produce a stable and persistent block of the receptor. The experiments were based on the principle that 5-HT combines with its receptor and protects the receptor from binding with phenoxybenzamine. The 5-HT-receptor was irreversibly blocked by phenoxybenzamine (3 .times. 10-7 g/ml). In normal Locke-Ringer solution, 5-HT (3 .times. 10-6 g/ml) protected its receptor from the block produced by phenoxybenzamine (3 .times. 10-7 g/ml). Similar results were obtained in Ca-free and Mg-free solution. Ca and/or Mg ions are involved in the 5-HT-receptor interaction and in the interactions of the other agonists with their receptors. Ca and Mg ions may induce conformation changes in the receptor. The 5-HT-receptor is postulated to exist under 2 conformations.