Role of carbon monoxide in electrically induced non-adrenergic, non-cholinergic relaxations in the guinea-pig isolated whole trachea.
OBJECTIVE
Nitric oxide (NO) and vasoactive intestinal peptide (VIP) are considered transmitters of non-adrenergic, non-cholinergic (NANC) relaxations in guinea-pig trachea, whereas the role of carbon monoxide (CO) is unknown. This study was designed to assess the participation of CO, and to investigate the localization of haem oxygenase-2 (HO-2), the CO-producing enzyme, in tracheal neurons.


METHODS
NANC responses to electrical field stimulation (EFS) at 3 and 10 Hz were evaluated in epithelium-free whole tracheal segments as intraluminal pressure changes. Drugs used were: L-nitroarginine methyl ester (L-NAME, 100 microM) to inhibit NO synthase (NOS), alpha-chymotrypsin (2 U ml(-1)) to inactivate VIP, zinc protoporphyrin-IX (ZnPP-IX, 10 microM) to inhibit HO-2, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), a soluble guanylyl cyclase inhibitor. For immunohistochemistry, tissues were exposed to antibodies to PGP 9.5, a general neuronal marker, HO-2 and NOS, and processed with an indirect immunofluorescence method.


RESULTS
alpha-Chymotrypsin did not affect NANC relaxations. ODQ inhibited NANC responses by about 60%, a value similar to that obtained by combining L-NAME and ZnPP-IX. The combination of ODQ, L-NAME and ZnPP-IX reduced the responses by 90%. Subpopulations of HO-2 positive neurons containing NOS were detected in tracheal sections.


CONCLUSIONS
In the guinea-pig trachea, NANC inhibitory responses at 3 and 10 Hz use NO and CO as main transmitters. Their participation is revealed following inhibition of NOS, HO-2 and soluble guanylyl cyclase. The involvement of CO as a relaxing transmitter paves the way for novel therapeutic approaches in the treatment of airway obstruction.
Dellabianca
A
A
Department of Preventive, Occupational and Community Medicine, University of Pavia, Pavia, Italy. antonio.dellabianca@unipv.it
Sacchi
M
M
Anselmi
L
L
De Amici
E
E
Cervio
E
E
Agazzi
A
A
Tonini
S
S
Sternini
C
C
Tonini
M
M
Candura
S M
SM
D000818:Animals; D002248:Carbon Monoxide / Q000502:physiology*; D004558:Electric Stimulation; D006168:Guinea Pigs; D006419:Heme Oxygenase (Decyclizing) / Q000502:physiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000502:physiology; D008297:Male; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology; D014132:Trachea / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000502:physiology
D007527:Isoenzymes; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; D002248:Carbon Monoxide; D006419:Heme Oxygenase (Decyclizing); C105245:heme oxygenase-2