Peptidoleukotriene binding in guinea pig uterine membrane preparations

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Abstract

Peptidoleukotrienes are known to be potent smooth muscle contractile agents in many tissues, including guinea pig uterus. In order to characterize the receptors at which the leukotrienes interact, guinea pig uteri were homogenized in 50nM Tris-HCl, pH 7.4 at 40°C and centrifuged at 1000xg fpr 10 min. The supernatant was centrifuged at 40,000 xg and the washed pellet was used to measure the binding of 3H-LTC4 and 3H-LTD4. Specific binding of 3H-LTD4 was not detected, but specific, saturable binding of 3H-LTC4 was measured at 40°C, was complete in 10 min. and was rapidly reversible on addition of unlabeled LTC4. Binding was linear with protein concentration and stimulated by CaCl2 and L-serine borate. Scatchard and kinetic analysis of binding in the presence of calcium suggested a Kd of 10–12 nM. LTC4 was a more potent competitor of binding than LTD4 (IC50 − 40nM and 30 μM, respectively). FPL 55712 inhibited binding from 10–100 μM but stimulated binding at lower concentrations. Thus, the guinea pig uterus has specific receptors for LTC4, but not LTD4, that can be demonstrated by radioligand binding.

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