Role of endothelium in vasomotor responses to endothelin system and protein kinase C activation in porcine retinal arterioles.
OBJECTIVE
Endothelial cells synthesize vasodilator nitric oxide (NO) and vasoconstrictor endothelin-1 (ET-1) from NO synthase (eNOS) and endothelin-converting enzyme-1 (ECE-1), respectively. Protein kinase C (PKC) and Rho kinase (ROCK) are major signaling molecules mediating vasoconstriction. Although endothelial cells express eNOS, ECE-1, endothelin B (ET(B)) receptors, PKC, and ROCK, their influences on ET-1-induced vasoconstriction remain elusive. We studied whether these endothelial signaling molecules modulate retinal arteriolar constriction to ET-1.


METHODS
Porcine retinal arterioles were isolated and pressurized for vasomotor study, under conditions with intact or denuded endothelium, using videomicroscopic techniques.


RESULTS
Retinal arterioles developed similar resting tone (≈45% of maximum diameter) with or without endothelium. Endothelial denudation attenuated vasoconstriction to ET-1 precursor, big ET-1, by almost equal to 50%, but did not affect vasoconstrictions to ET-1, ET(B) agonist sarafotoxin S6c, or PKC activator phorbol-12, 13-dibutyrate (PDBu). The ROCK inhibitor H-1152 caused vasodilation, and abolished vasoconstrictions to ET-1 and PDBu independent of endothelium. With L-type voltage-operated calcium channel (L-VOCC) blocker nifedipine, PDBu-induced vasoconstriction was abolished and converted to NO-mediated vasodilation in the presence of endothelium. The ET-1-induced vasoconstriction was unaffected by NO released from endothelium during flow elevation.


CONCLUSIONS
Endothelial and smooth muscle ECE-1 contribute equally to synthesis of vasoactive ET-1 in retinal arterioles, with nominal role of endothelial ETB receptors in vasoconstriction to ET-1. The PKC activation leads to endothelium-dependent NO-mediated vasodilation when smooth muscle contraction is ablated by L-VOCC blockade. Endothelial cells and NO appear to have modest roles in modulating ROCK-dependent vasoconstriction, and are insufficient to counteract smooth muscle contractions to ET-1 and PKC activation.
Department of Medical Physiology, Scott & White Healthcare, College of Medicine, Texas A&M Health Science Center, Temple, Texas.
Luke B
LB
Potts
Patrick D
PD
Bradley
Wenjuan
W
Xu
Lih
L
Kuo
Travis W
TW
Hein
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000502:physiology; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism; D003646:Debridement; D019332:Endothelin-1 / Q000494:pharmacology*; D000072396:Endothelin-Converting Enzymes; D004730:Endothelium, Vascular / Q000502:physiology*; D004789:Enzyme Activation; D005260:Female; D008297:Male; D008666:Metalloendopeptidases / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012161:Retinal Artery / Q000502:physiology*; D034421:Sus scrofa; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology; D014666:Vasomotor System / Q000187:drug effects*; D014757:Viper Venoms / Q000494:pharmacology
C459092:2-methyl-1-((4-methyl-5-isoquinolinyl)sulfonyl)homopiperazine; D019332:Endothelin-1; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D014757:Viper Venoms; C057354:sarafotoxins s6; D015240:Phorbol 12,13-Dibutyrate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D016282:Aspartic Acid Endopeptidases; D008666:Metalloendopeptidases; D000072396:Endothelin-Converting Enzymes
PKC; arterioles; endothelins; endothelium; retinal blood flow