CHARACTERISTICS OF THE BRADYKININ-INDUCED CHANGES IN INTRACELLULAR CALCIUM-ION CONCENTRATION OF SINGLE BOVINE TRACHEAL SMOOTH-MUSCLE CELLS

1 Single bovine tracheal smooth muscle (BTSM) cells were cultured and used to 2 Bradykinin (10 pm- 10 mum)-induced an increase in [Ca2+]i over basal levels (69 +/- 2 nm; n = 353) which was concentration-dependent (log EC50 = - 8.7 M) in the presence of extracellular calcium ions (2 mM). The bradykinin B2 receptor antagonist, D-Arg[Hyp3,Thi5,8,D-Phe7]-bradykinin, produced a parallel shift to the right of the bradykinin concentration-response curve (log EC50 = - 7.1 M and - 5.8 m in the presence of 1 mum and 10 mum antagonist respectively) yielding an apparent K(D) of 26 nm. 3 In the absence of extracellular calcium ions (with 0. 1 mm EGTA), bradykinin (I 0 pm- 10 mum) produced a uniform increase in [Ca2+]i from a basal level of 33 +/- 2 nm (n = 140) to approximately 180 nm in BTSM cells indicating an 'all-or-nothing' release of intracellular calcium ions. In the presence of 10 muM D-Arg[Hyp3,Thi5,8,D-Phe7]-bradykinin no responses could be induced by bradykinin at concentrations below 100 nm. However, at 100 nm and 1 mum bradykinin there was no change in the uniform increase in [Ca2+], in these cells previously observed. 4 In both the absence or presence Of D-Arg[Hyp3, Thi5,8,D-Phe 7]-bradykinin, there was a concentration-dependent increase in the percentage of cells responding to bradykinin (frequency) under calcium-rich or calcium-free conditions. Individual cells also demonstrated a difference in the sensitivity to any particular concentration of bradykinin. 5 A latency in the response of cells to bradykinin was observed both in calcium-containing and calcium-free conditions. 6 We conclude that bradykinin B2 receptors are expressed by BTSM cells and are involved in the bradykinin-induced increase in [Ca2+]i. It appears that the increase in [Ca2+]i can be mediated via a graded influx of calcium ions from the extracellular space or an 'all-or-nothing' release from intracellular stores.