Mechanisms of leukotriene D4-induced constriction in human small bronchioles.
We examined the mechanisms underlying leukotriene D4- (LTD4) induced constriction of human small (300 - 500 micron i.d.) bronchioles, and the effect of LTD4 on ion currents and Ca2+ transients in smooth muscle cells (SMC) isolated from these bronchioles. LTD4 caused a concentration-dependent bronchoconstriction with an EC50=0.58+/-0.05 nM (n=7) which was not easily reversible upon washout. This bronchoconstriction was entirely dependent on extracellular Ca2+. Blockade of L-type Ca2+ channels with nifedipine (10 microM) reduced LTD4 response by 39+/-2% (n=8), whilst La3+, Gd3+ and SK&F 96,365 abolished LTD4-induced bronchoconstriction completely and reversibly, suggesting the majority of Ca2+ entry was via non-selective cation channels. Antagonists of PI-PLC (U73,122 and ET-18-OCH3), PLD (propranolol) and PKC (cheleretrine and Ro31-8220) were without any effect on LTD4-induced bronchoconstriction, whilst the PC-PLC inhibitor D609 caused complete relaxation. Inhibition of protein tyrosine kinase with tyrphostin A23 (100 microM) caused about 50% relaxation, although the inactive analogue tyrphostin A1 was without effect. In freshly isolated SMC from human small bronchioles LTD4 caused a slow increase of intracellular Ca2+ concentration, with a consequent rise of the activity of large conductance Ca2+-dependent K+ channels and the amplitude of depolarization-induced outward whole-cell current. Again, no effect of LTD4 could be observed in the absence of extracellular Ca2+. We conclude that LTD4 causes constriction of these small bronchioles primarily by activating Ca2+ entry via non-voltage gated channels, possibly by a PC-PLC mediated pathway.
Snetkov
V A
VA
Department of Respiratory Medicine and Allergy, Guy's, King's and St Thomas' School of Medicine, King's College London, Guy's Campus, London SE1 9RT. vladimir.snetkov@kcl.ac.uk
Hapgood
K J
KJ
McVicker
C G
CG
Lee
T H
TH
Ward
J P
JP
D000368:Aged; D000369:Aged, 80 and over; D001980:Bronchi / Q000166:cytology / Q000187:drug effects*; D016084:Bronchoconstriction / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002469:Cell Separation; D004594:Electrophysiology; D006801:Humans; D066298:In Vitro Techniques; D017998:Leukotriene D4 / Q000494:pharmacology*; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects; D018408:Patch-Clamp Techniques
D017998:Leukotriene D4; D002118:Calcium