A high-affinity bradykinin receptor in membranes from rat myometrium is coupled to pertussis toxin-sensitive G-proteins of the Gi family

In rat myometrial membranes, two 3H-Bradykinin binding sites with KD values of 16 pM and 1.0 nM were identified. Employed at pM concentrations, bradykinin stimulated high affinity GTPases. This effect was abolished by the bradykinin antagonist, [D-Arg(Hyp3-Thi5,8, D-Phe7)]bradykinin (10 μM), and by treatment of membranes with pertussis toxin. Myometrial membranes contained two pertussis toxin substrates of 40 and 41 kDa, which corresponded immunologically to α-subunits of Gi-type G-proteins. The faster migrating substrate was tentatively identified as Gi2 α-subunit. The electrophoretic mobility of the slower migrating Gi α-subunit was very similar to that of the Gi3 α-subunit. Go α-subunits were not detected. Thus, in uterine smooth muscle, G-proteins of the Gi-family (Gi2, Gi3) couple high-affinity bradykinin receptors to their effector enzymes.