G. Edwards et al., Further investigations into the endothelium-dependent hyperpolarizing effects of bradykinin and substance P in porcine coronary artery, BR J PHARM, 133(7), 2001, pp. 1145-1153
1 In porcine coronary arteries, smooth muscle hyperpolarizations produced b
y the nitric oxide donor, NOR-1, and the prostacyclin analogue, iloprost, w
ere compared with those induced by substance P and bradykinin and attribute
d to the endothelium-derived hyperpolarizing factor (EDHF).
2 In the presence of 300 muM L-nitroarginine and 10 muM indomethacin, ilopr
ost-induced hyperpolarizations were partially inhibited by 10 muM glibencla
mide whereas those to NOR-1, substance P and bradykinin were unaffected.
3 Hyperpolarizations produced by maximally-effective concentrations of NOR-
1 and NS1619 were identical (to -65 mV). They were significantly less than
those generated by either substance P or bradykinin (to approximately -80 m
V) and were abolished by iberiotoxin 100 nM, a concentration which had esse
ntially no effect on responses to substance P or bradykinin.
4 Incubation of segments of intact arteries for 16 - 22 h in bicarbonate-bu
ffered Krebs solution had little effect on EDHF responses to substance P or
bradykinin. In contrast, after incubation for this period of time in HEPES
-buffered Tyrode solution or Krebs containing 10 mm HEPES the EDHF response
to substance P was abolished and that to bradykinin was markedly reduced.
The residual bradykinin-induced hyperpolarization following incubation in T
yrode solution was inhibited by iberiotoxin and by 10 muM 17-octadecynoic a
cid.
5 We conclude that substance P activates only the EDHF pathway in the prese
nce of nitric oxide synthase and cyclo-oxygenase inhibitors. Incubation in
HEPES-buffered Tyrode solution abolishes the EDHF responses to substance P
and bradykinin to reveal an additional hyperpolarizing mechanism, associate
d with the opening of K+ channels, activated only by bradykinin.