Dominant role of an endothelium‐derived hyperpolarizing factor (EDHF)‐like vasodilator in the ciliary vascular bed of the bovine isolated perfused eye

Abstract

1 The roles of the endothelium-derived nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor (EDHF) in mediating vasodilator responses to acetylcholine and bradykinin were assessed in the ciliary vascular bed of the bovine isolated perfused eye preparation. 2 Vasodilatation to acetylcholine or bradykinin was una ected by the nitric oxide synthase inhibitor, L-NAME (100 mM), or the cyclo-oxygenase inhibitor,¯urbiprofen (30 mM), but was virtually abolished following treatment with a high concentration of KCl (30 mM), or by damaging the endothelium with the detergent, CHAPS (0.3%, 2 min). 3 Acetylcholine-induced vasodilatation was una ected by glibenclamide (10 mM), an inhibitor of ATP-sensitive K + channels (K + ATP ), but was signi®cantly attenuated by TEA (10 mM), a nonselective inhibitor of K + channels. 4 The small conductance calcium-sensitive K + channel (SK + Ca ) inhibitor, apamin (100 nM), and the large conductance calcium-sensitive K + channel (BK + Ca ) inhibitor, iberiotoxin (50 nM), had no signi®cant e ect on acetylcholine-induced vasodilatation. In contrast, the intermediate (IK + Ca )/large conductance calcium-sensitive K + channel inhibitor, charybdotoxin (50 nM), powerfully blocked these vasodilator responses, and uncovered a vasoconstrictor response. 5 The combination of apamin (100 nM) with a sub-threshold concentration of charybdotoxin (10 nM) signi®cantly attenuated acetylcholine-induced vasodilatation, but the combination of apamin (100 nM) with iberiotoxin (50 nM) had no e ect. 6 In conclusion, blockade by a high concentration of KCl, by charybdotoxin, or by the combination of apamin with a sub-threshold concentration of charybdotoxin, strongly suggests that vasodilatation in the bovine isolated perfused eye is mediated by an EDHF. British Journal of Pharmacology (2001) 134, 912 ± 920

Enhanced endothelium derived hyperpolarising factor activity in resistance arteries from normal pressure glaucoma patients: implications for vascular function in the eye

“…COX inhibition (with meclofenamic acid) had no further effect, supporting previous evidence that prostaglandins do not contribute to relaxation in these vessels. 20 Residual relaxation was abolished, however, by the combination of SK Ca and IK Ca blockers (apamin and charybdotoxin, respectively). This supports the suggestion that EDHF makes a significant contribution to relaxation of the porcine ciliary artery.…”

Thromboxane receptor stimulation associated with loss of SKCa activity and reduced EDHF responses in the rat isolated mesenteric artery

“…In this regard, the use of U46619 is fairly widespread, as it causes stable contraction (Parkington et al, 1995;McNeish et al, 2001;Bauersachs et al, 2002). Interestingly, in the study by McNeish et al (2001), only the IK Ca blocker charybdotoxin was required to abolish EDHF dilatation in the bovine ciliary vascular bed. The apparent absence of SK Ca -evoked hyperpolarization in these vessels might then reflect their selective loss due to stimulation with U46619.…”

“…The ability of TXA 2 potently to stimulate sustained background contraction of vascular smooth muscle is also commonly employed in studies investigating endothelium-dependent dilator pathways (e.g. Fisslthaler et al, 1999;McNeish et al, 2001). However, stimulation of resistance arteries with high concentrations of the TXA 2 mimetic U46619 is associated with a selective loss of the subsequent relaxation caused by endothelium-derived hyperpolarizing factor (EDHF; Plane & Garland, 1996).…”

Ascorbate blocks endothelium‐derived hyperpolarizing factor (EDHF)‐mediated vasodilatation in the bovine ciliary vascular bed and rat mesentery

“…The ciliary vascular bed of the bovine eye was perfused using the constant flow method as previously described (McNeish et al ., 2001). In brief, bovine eyes obtained from a local abattoir within 1 h of killing were cannulated through a long posterior ciliary artery and perfused at 37°C with Krebs solution containing (m M ): NaCl, 118; KCl, 4.7; CaCl 2 , 2.5; KH 2 PO 4 , 1.2; MgSO 4 1.2; NaHCO 3 , 25; glucose, 11.5; and gassed with O 2 containing 5% CO 2 .…”

“…More recently, we have begun to study the bovine ciliary vascular bed and have found that nitric oxide exerts a small tonic vasodilator action, but it plays no part in the powerful endothelium‐dependent vasodilator responses induced by acetylcholine or bradykinin in this preparation (McNeish et al ., 2001). These vasodilator responses are, however, blocked by depolarizing solutions of KCl and by charybdotoxin (McNeish et al ., 2001) and thus have the characteristics of the endothelium‐derived hyperpolarizing factor (EDHF; for reviews see Feletou & Vanhoutte, 1999; Campbell & Harder, 2001).…”