PURPOSE In normotensive eyes, reduced ocular blood flow can lead to glaucoma pathogenesis. Drugs that reduce intraocular pressure (IOP) often cause vasodilation of the ciliary arteries and improve blood flow to the eye. A novel class of drugs called Rho-associated coiled coil-forming protein kinase (ROCK) inhibitors can lower IOP. Therefore, we tested the ability of two ROCK inhibitors, Y-27632 and Y39983, to relax rabbit ciliary arteries. METHODS We measured in vitro ciliary artery smooth muscle contractions by isometric tension recordings and changes of intracellular free calcium concentration ([Ca(2+)](i)) by fluorescence photometry. RESULTS Both Y-27632 and Y-39983 induced a concentration-dependent relaxation in rabbit ciliary arteries precontracted with a high-potassium (high-K) solution. The amplitude of relaxation induced by Y-27632 and Y-39983 was not affected by either 100 μM N (G)-nitro-L:-arginine methyl ester (L:-NAME) or 10 μM indomethacin. In Ca(2+)-free solution, Y-27632 and Y-39983 significantly inhibited the transient contraction of ciliary arteries induced by 10 μM histamine. However, neither Y-27632 nor Y-39983 affected the elevation of [Ca(2+)](i) induced by high-K solution and histamine. CONCLUSIONS We concluded that Y-27632 and Y-39983 relaxed isolated rabbit ciliary artery segments in vitro. The mechanism of relaxation was not dependent on endothelial-derived factors such as nitric oxide (NO) or prostacyclin, nor was it dependent on changes in intracellular Ca(2+) concentration.

Vascular peripheral resistance is increased during hypertension, and endothelium-derived hyperpolarizing factor (EDHF) is an important for regulating vasodilation in small arteries. Therefore we characterized the role of EDHF in regulating vascular resistance of ocular ciliary arteries from spontaneous hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Isometric tension recordings were used in isolated ocular ciliary artery segments from SHR and WKY. Ocular ciliary arteries pre-contracted with 100 muM norepinephrine exhibited a concentration-dependent relaxation to acetylcholine, and the effect on SHR arteries was smaller than that on WKY arteries (P<0.05). The EDHF-mediated component of this relaxation, determined in the presence of 100 muM L-NAME plus 10 muM indomethacin, was also smaller in SHR than in WKY arteries (P<0.05). Apamin (1 muM), a blocker of small-conductance calcium-activated K(+)(K(Ca)) channels, had no effect on EDHF-mediated relaxation in either preparation. However, charybdotoxin (0.1 muM), which blocks intermediate- and large-conductance K(Ca) channels, and iberiotoxin (0.1 muM), which blocks large-conductance K(Ca) channels, almost completely suppressed EDHF-mediated relaxation in both preparations. The tension of ciliary arteries from both SHR and WKY was increased above baseline by 100 muM L-NAME plus 10 muM indomethacin. In these preparations, apamin had no effect on the tension in arteries from either SHR or WKY. However, both charybdotoxin and iberiotoxin further increased tension above that induced by L-NAME and indomethacin. The increase was smaller for SHR than WKY (P<0.05). In summary, the ability of EDHF to relax ocular ciliary artery vascular tone in SHR is smaller than in WKY. The large-conductance calcium-activated K(+) channel is utilized in EDHF signaling pathway.

Vascular peripheral resistance is increased during hypertension, and endothelium-derived hyperpolarizing factor (EDHF) is an important for regulating vasodilation in small arteries. Therefore we characterized the role of EDHF in regulating vascular resistance of ocular ciliary arteries from spontaneous hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). Isometric tension recordings were used in isolated ocular ciliary artery segments from SHR and WKY. Ocular ciliary arteries pre-contracted with 100 muM norepinephrine exhibited a concentration-dependent relaxation to acetylcholine, and the effect on SHR arteries was smaller than that on WKY arteries (P<0.05). The EDHF-mediated component of this relaxation, determined in the presence of 100 muM L-NAME plus 10 muM indomethacin, was also smaller in SHR than in WKY arteries (P<0.05). Apamin (1 muM), a blocker of small-conductance calcium-activated K(+)(K(Ca)) channels, had no effect on EDHF-mediated relaxation in either preparation. However, charybdotoxin (0.1 muM), which blocks intermediate- and large-conductance K(Ca) channels, and iberiotoxin (0.1 muM), which blocks large-conductance K(Ca) channels, almost completely suppressed EDHF-mediated relaxation in both preparations. The tension of ciliary arteries from both SHR and WKY was increased above baseline by 100 muM L-NAME plus 10 muM indomethacin. In these preparations, apamin had no effect on the tension in arteries from either SHR or WKY. However, both charybdotoxin and iberiotoxin further increased tension above that induced by L-NAME and indomethacin. The increase was smaller for SHR than WKY (P<0.05). In summary, the ability of EDHF to relax ocular ciliary artery vascular tone in SHR is smaller than in WKY. The large-conductance calcium-activated K(+) channel is utilized in EDHF signaling pathway.