Constriction of Retinal Venules to Endothelin-1: Obligatory Roles of ET_A Receptors, Extracellular Calcium Entry, and Rho Kinase

Abstract

PurposeEndothelin-1 (ET-1) is a potent vasoconstrictor peptide implicated in retinal venous pathologies such as diabetic retinopathy and retinal vein occlusion. However, underlying mechanisms contributing to venular constriction remain unknown. Thus, we examined the roles of ET-1 receptors, extracellular calcium (Ca2+), L-type voltage-operated calcium channels (L-VOCCs), Rho kinase (ROCK), and protein kinase C (PKC) in ET-1-induced constriction of retinal venules.MethodsPorcine retinal venules were isolated and pressurized for vasoreactivity study using videomicroscopic techniques. Protein and mRNA were analyzed using molecular tools.ResultsRetinal venules developed basal tone and constricted concentration-dependently to ET-1. The ETA receptor (ETAR) antagonist BQ123 abolished venular constriction to ET-1, but ETB receptor (ETBR) antagonist BQ788 had no effect on vasoconstriction. The ETBR agonist sarafotoxin S6c did not elicit vasomotor activity. In the absence of extracellular Ca2+, venules lost basal tone and ET-1–induced constriction was nearly abolished. Although L-VOCC inhibitor nifedipine also reduced basal tone and blocked vasoconstriction to L-VOCC activator Bay K8644, constriction of venules to ET-1 remained. The ROCK inhibitor H-1152 but not PKC inhibitor Gö 6983 prevented ET-1-induced vasoconstriction. Protein and mRNA expressions of ETARs and ETBRs, along with ROCK1 and ROCK2 isoforms, were detected in retinal venules.ConclusionsExtracellular Ca2+ entry via L-VOCCs is essential for developing and maintaining basal tone of porcine retinal venules. ET-1 causes significant constriction of retinal venules by activating ETARs and extracellular Ca2+ entry independent of L-VOCCs. Activation of ROCK signaling, without involvement of PKC, appears to mediate venular constriction to ET-1 in the porcine retina.

Endothelin 1-induced retinal ganglion cell death is largely mediated by JUN activation

“…The canonical role of the EDN system is to mediate vasoconstriction. EDN ligands are the most potent vasoactive peptides, and EDN has been shown to cause vasoconstriction through EDNRA expressed by vascular smooth muscle cells 4,7,8,43,44 . Importantly, JUN-JNK signaling has been shown to mediate neuronal death after ischemic insult [47][48][49][50][51] .…”

“…In addition to the apoptotic RGC-autonomous mechanisms triggered by EDN signaling, the cell types that respond to EDN ligands to ultimately cause RGC death remain unknown. EDN ligands cause vasoconstriction by binding to EDNRA expressed by vascular smooth muscle cells 4,7,8,43,44 . Thinner retinal vessels and evidence of hypoxia have been demonstrated in animal models of chronic glaucoma 5,6,45,46 .…”

Hyperglycemia Augments Endothelin-1–Induced Constriction of Human Retinal Venules

“…22,23 Our previous study found that ET-1 causes marked constriction of porcine retinal venules through ET A receptors (ET A Rs) and extracellular Ca 2+ influx independent of L-type voltage-operated Ca 2+ channels. 20 We have also shown that hyperglycemia, a hallmark of diabetes, augments porcine venular constrictions to ET-1, U46619, and norepinephrine. 21 However, there has been no study addressing whether ET-1 affects the vasomotor tone of human retinal venules under euglycemia or hyperglycemia.…”

“…Techniques for identifying and isolating human and porcine retinal microvessels were similar to those used in our previous studies. 20,21,28 Briefly, retinal venules (1.0-1.5 mm in length without side branches) were identified based on the dark red deoxygenated blood in The sex, cardiovascular diseases, and medications and supplements to treat these diseases are provided for the five patients who donated retinal tissue for the vascular studies. the lumen and their thin vascular wall compared with the parallel arterioles containing bright red oxygenated blood and a thick vascular wall.…”

“…17,18 Constriction of retinal venous vessels leads to an increased retinal venous pressure, which could subsequently decrease retinal perfusion and promote capillary fluid filtration (i.e., edema) when compensatory or defense mechanisms are exhausted in the earlier stages of diabetes before the development of retinopathy. However, our understanding of factors directly affecting the vasomotor activity of retinal venules is seemingly limited to three studies in pigs, [19][20][21] which resemble human retinal morphology and structure. 22,23 Our previous study found that ET-1 causes marked constriction of porcine retinal venules through ET A receptors (ET A Rs) and extracellular Ca 2+ influx independent of L-type voltage-operated Ca 2+ channels.…”