Essential role of Gap junctions in NO- and prostanoid-independent relaxations evoked by acetylcholine in rabbit intracerebral arteries.
OBJECTIVE
Direct intercellular communication via gap junctions may play a central role in endothelium-dependent relaxations that are mediated by a conducted hyperpolarization and do not involve the synthesis of NO and prostanoids. In the present study, inhibitory peptides homologous to the Gap27 domain of the second extracellular loop of connexin37/connexin43 and connexin40, designated as 37,43Gap27 and 40Gap27, respectively, were used to evaluate the role of this mechanism in intracerebral arteries.


METHODS
Isolated rings of rabbit middle cerebral artery were constricted by histamine (10 micromol/L) in the presence of N(G)-nitro-L-arginine methyl ester (300 micromol/L) and indomethacin (10 micromol/L). Concentration-relaxation curves for acetylcholine were constructed in the presence and absence of 37,43Gap27 and 40Gap27. Specific antibodies were used to delineate the distribution of connexin37, connexin40, connexin43, and connexin45 within the arterial wall.


RESULTS
Individually, 37,43Gap27 and 40Gap27 minimally affected endothelium-dependent relaxations to acetylcholine at concentrations of 300 micro mol/L, whereas their combination (at 300 micromol/L each) inhibited the maximal response by approximately 70% and increased the EC50 value for relaxation by approximately 15-fold. In endothelium-denuded rings, this peptide combination did not attenuate responses to sodium nitroprusside, an exogenous source of NO. Gap junction plaques, whose incidence was highest in endothelium, were constructed from connexin40 and connexin43 in the media and connexin37, connexin40, and connexin43 in the endothelium.


CONCLUSIONS
The findings confirm that direct communication via gap junctions contributes to agonist-induced relaxations of intracerebral arteries. More than one connexin subtype appears to participate in such responses.
Ujiie
Hiroshi
H
Department of Diagnostic Radiology, Wales Heart Research Institute, University of Wales College of Medicine, Heath Park, Cardiff, UK.
Chaytor
Andrew T
AT
Bakker
Linda M
LM
Griffith
Tudor M
TM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D017630:Connexins / Q000096:biosynthesis / Q000737:chemistry; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017629:Gap Junctions / Q000502:physiology*; D006632:Histamine / Q000494:pharmacology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D020768:Middle Cerebral Artery / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D011453:Prostaglandins / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D011817:Rabbits; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D017630:Connexins; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D010455:Peptides; D011453:Prostaglandins; D014665:Vasodilator Agents; D009569:Nitric Oxide; D006632:Histamine; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin