Bradykinin B2 receptor‐mediated phosphoinositide hydrolysis in bovine cultured tracheal smooth muscle cells

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Abstract
1 Bovine tracheal smooth muscle cells were established in culture to study agonist-induced phosphoinositide (PI) hydrolysis in this tissue. 2 Bradykinin (0.1 nm-10 μm) evoked a concentration-dependent increase (log EC50 (m) = −9.4 ±0.2; n = 8) in the accumulation of total [3H]-inositol phosphates in cultured tracheal smooth muscle cells whereas the selective B1 receptor agonist des-Arg9-bradykinin (10 μm) was significantly less effective (16% of bradykinin maximal response; relative potency = 0.2 with respect to bradykinin = 100). 3 The bradykinin-induced increase in PI hydrolysis was unaffected by the B1 receptor antagonist des-Arg9[Leu8]-bradykinin (1 nm-1 μm) but showed marked attenuation in the presence of the B2 receptor antagonists d-Arg,[Hyp3,d-Phe7]-bradykinin (10 nm-10 μm) or d-Arg[Hyp3,Thi5,8,d-Phe7]-bradykinin (10 nm-10 μm). The estimated KB values obtained for these two compounds, assuming competitive antagonism, were 40 ± 14 nm and 8.6 ± 2.8 nm for d-Arg,[Hyp3,d-Phe7]-bradykinin and d-Arg[Hyp3,Thi5,8,d-Phe7]-bradykinin respectively. 4 We conclude that bradykinin B2 receptors are expressed in cultured bovine tracheal smooth muscle cells and are coupled to PI hydrolysis mechanisms.