Role of endothelium in vasomotor responses to endothelin system and protein kinase C activation in porcine retinal arterioles.
PURPOSE
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.
['Potts|Luke B|LB|', 'Bradley|Patrick D|PD|', 'Xu|Wenjuan|W|', 'Kuo|Lih|L|', 'Hein|Travis W|TW|']
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine D000818:Animals D001160:Arterioles D016282:Aspartic Acid Endopeptidases D003646:Debridement D019332:Endothelin-1 D000072396:Endothelin-Converting Enzymes D004730:Endothelium, Vascular D004789:Enzyme Activation D005260:Female D008297:Male D008666:Metalloendopeptidases D009131:Muscle, Smooth, Vascular D015240:Phorbol 12,13-Dibutyrate D011493:Protein Kinase C D012161:Retinal Artery D034421:Sus scrofa D014662:Vasoconstrictor Agents D014665:Vasodilator Agents D014666:Vasomotor System D014757:Viper Venoms
endothelium endothelins arterioles PKC retinal blood flow