The Effects of Prostaglandin Analogues on Intracellular Ca2+ in Ciliary Arteries of Wild-Type and Prostanoid Receptor-Deficient Mice

Purpose: To clarify the mechanism of prostaglandin (PG) analogue-dependent relaxation in ciliary arteries from wild-type (WT) and prostanoid receptor-deficient mice. Methods: The intracellular-free calcium concentration ([Ca2+](i)) in isolated WT mouse ciliary arteries was measured by fluorescence photometry. Reduction of [Ca2+](i) leading to vascular relaxation by PG analogues latanoprost, isopropyl unoprostone, or tafluprost was compared to the maximum increase of [Ca2+](i) by 50 mM KCl. The cyclooxygenase inhibitor indomethacin and the NO synthase inhibitor N-G-nitro-(L)-arginine methylester ((L)-NAME) were added to investigate the involvement of vascular endothelial factors. Moreover, PG analogue-dependent reduction of [Ca2+](i) was measured in ciliary artery strips from FP, EP1, EP2, and EP3 receptor-deficient mice. Results: The 3 PG analogues reduced K+-dependent increase in [Ca2+](i) in a concentration-dependent manner. Indomethacin (10 mu M) had little effect. The reductions of [Ca2+](i) induced by 10 mu M PG analogues were not significantly affected by the treatment with the NO synthase inhibitor L-NAME (10(-4) M). The effect of all 3 PG analogues in FP and EP3 receptor-deficient arteries was similar to the effect in WT arteries. Latanoprost significantly enhanced the reduction of [Ca2+](i) in ciliary arteries from prostanoid EP1 and EP2 receptor-deficient mice compared to WT mice. Tafluprost had a similar effect in arteries from EP2 receptor-deficient mice. Conclusions: PG analogues latanoprost, isopropyl unoprostone, and tafluprost reduced the K+-dependent increase in [Ca2+](i) in isolated mouse ciliary arteries. Endothelial-derived factors and FP and EP3 receptors were not involved in the responses. The increased effectiveness of latanoprost and tafluprost in reducing [Ca2+](i) in EP1 and EP2 receptor-deficient arteries suggests that the PG analogues may act, at least partially, through nonprostanoid receptor pathways. For glaucoma patients, PG analogues can be selected to reduce the intraocular pressure and increase the ocular blood flow.