Leukotriene D4-induced activation of smooth-muscle cells from human bronchi is partly Ca2+-independent.
Cysteine-containing leukotrienes (cysteinyl-LTs) are potent bronchoconstrictors and play a key role in asthma. We found that histamine and LTD4 markedly constrict strips of human bronchi (HB) with similar efficacy. However, in human airway smooth-muscle (HASM) cells, LTD4, at variance with histamine, elicited only a small, transient change in intracellular calcium ion concentration. HASM cells express both Ca2+-dependent and -independent isoforms of protein kinase C (PKC) (i.e., PKC-alpha and PKC-alpha ). Western blot analysis showed that PKC-alpha is activated by histamine and, to a lesser extent, by LTD4, whereas only LTD4 translocates PKC-alpha. This translocation was specifically inhibited by the LTD4 antagonist pobilukast. Phorbol-dibutyrate ester (PDBu) (a PKC activator) contracted HB strips to the same extent in the presence as in the absence of extra- and intracellular Ca2+. In the absence of Ca2+, LTD4 contracted HB strips to the same extent as did PDBu, suggesting the involvement of a Ca2+-independent PKC in LTD4-mediated signal transduction. PDBu-induced desensitization and the PKC inhibitor H7 abolished the slow and sustained LTD4-triggered contraction of HB strips in the absence of Ca2+, although H7 did not greatly affect the response in the presence of the ion. Thus, in human airways, we identified a novel LTD4 transduction mechanism linked to bronchial smooth-muscle contraction, which is partly independent of Ca2+ and involves the activation of PKC-alpha.
Accomazzo
M R
MR
Institute of Pharmacological Sciences, and Department of Biotechnology and Biosciences, University of Milan, Italy.
Rovati
G E
GE
Viganò
T
T
Hernandez
A
A
Bonazzi
A
A
Bolla
M
M
Fumagalli
F
F
Viappiani
S
S
Galbiati
E
E
Ravasi
S
S
Albertoni
C
C
Di Luca
M
M
Caputi
A
A
Zannini
P
P
Chiesa
G
G
Villa
A M
AM
Doglia
S M
SM
Folco
G
G
Nicosia
S
S
D001980:Bronchi / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D006801:Humans; D017998:Leukotriene D4 / Q000502:physiology*; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000737:chemistry / Q000166:cytology* / Q000502:physiology*; D011493:Protein Kinase C / Q000032:analysis
D017998:Leukotriene D4; D011493:Protein Kinase C; D002118:Calcium