Purchase this article with an account.
X. Liu, D.E. Kourennyi; Concentration Dependent Effects of Nitric Oxide on Rod Photoreceptors . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4160.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study the effects of different concentrations of nitric oxide (NO) on calcium channels in rod photoreceptor. Methods: Isolated rods from the retina of tiger salamander (Ambystoma tigrinum) were used in patch clamp and calcium fluorescence imaging experiments. The animals were handled and sacrificed according to the protocol approved by the University IACUC. The activation parameters of the barium current through calcium channels (the maximum conductance, Gmax, the half activation potential, V1/2, and the slope factor, S) were measured in different concentrations of NO donor S-nitrosocysteine (SNC) and compared to the control values. In separate experiments, calcium level in rod inner segment was measured using fura-2 ratiometric fluorescence imaging. The cells were slightly depolarized using 8-12 mM potassium solution resulting in an activation of calcium channels and the entry of calcium. At these depolarization levels, the steady-state calcium signal could be achieved, and the effect of SNC was evaluated. Results: We confirmed our previous findings that rod calcium channels are facilitated by high concentration of SNC (2 mM) by shifting V1/2 negatively with a slight increase in Gmax. In contrast, low concentrations of SNC (0.04-0.1 mM) shifted V1/2 to positive potentials. Intermediate concentrations of SNC (0.5-1 mM) did not seem to produce noticeable shift in V1/2. Interestingly, Gmax was still increased. Calcium entry was increased by high (2 mM) and intermediate concentration of SNC (0.5 mM), while it was suppressed by low concentration of SNC (0.1 mM). A suppression of calcium entry by low concentration of SNC is consistent with the positive shift in the calcium channel activation. An increase of calcium entry at intermediate concentration of SNC can be explained by an increase in Gmax. Conclusion: Our results show that NO affects calcium channels in photoreceptors in different ways depending on its concentration. The concentration dependency might indicate different molecular mechanisms involved in the effects of NO on calcium channels. Our findings introduce interesting possibilities to signal processing in the outer retina, especially taking into account that NO synthase is a calcium-dependent enzyme.
This PDF is available to Subscribers Only