Intraretinal calcium channels and retinal morbidity in experimental retinopathy of prematurity

Abstract

Purpose: To test the hypothesis that intraretinal calcium channels participate in retinal morbidity in a variable oxygen (VO) model of retinopathy of prematurity.

Methods: In control and VO Long Evans (LE) rats, either untreated or treated with voltage- or ligand-gated calcium channel antagonists, we measured retinal neovascular (NV) incidence and severity (adenosine diphosphatase staining), and retinal thickness and intraretinal ion channel activity (manganese-enhanced magnetic resonance imaging). Comparisons with the commonly studied Sprague Dawley rats were performed. Visual performance (optokinetic tracking) in untreated VO LE rats was also evaluated.

Results: In control LE rats, specific L-type voltage calcium channel antagonism, but not ligand-gated channel blockers, suppressed retinal manganese accumulation, while the inhibition of L-type channels normalized intraretinal uptake in VO LE rats. VO LE rats developed more severe NV than VO Sprague Dawley rats. Following VO, both strains demonstrated significant and similar degrees of retinal thinning and supernormal intraretinal manganese uptake. However, over time, intraretinal uptake remained elevated only in VO LE rats. Visual performance was subnormal in VO LE rats. L-type voltage-gated calcium channel antagonism reduced NV severity by 28% (p<0.05) in experimental LE rats compared to that in the control group.

Conclusions: Abnormal intraretinal calcium channel activity is linked with retinal morbidity in experimental retinopathy of prematurity.

Figure 1

Summary of antagonists on intraretinal manganese uptake. Systemically administered antagonists were N-Methyl-D-aspartate (NMDA) receptor (MK-801 [MK]), 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl)propanoic acid (AMPA) receptor (3-dihydroxy-6-nitro-7- sulfamoyl-benzo[f]quinoxaline-2,3-dione [NBQX; NB]), and L-type voltage-gated calcium channel (nifedipine (NIF)). Graphs depict A: Inner retina (IR) and B: Outer retina (OR) of dark adapted postnatal (P)50 Long Evans (LE) rats. The red line indicates a significant (p<0.05) difference from control values. Error bars represent standard error of the mean (SEM), and numbers above the bars represent the number of animals studied.

Figure 2

Summary of intraretinal manganese uptake time course data. Data are presented for outer retina as a percent change from age-controls (dotted orange line) for A: Sprague Dawley (SD) rats and B: variable oxygen (VO) rats. Inner retinal (IR) patterns were similar to these (outer retina) OR patterns. See Table 1 for numbers of rats investigated (n’s). Percent change from mean control and variable oxygen (VO) groups were calculated after subtraction of mean nonmanganese baseline values (50 arbitrary units (a.u.) for 4.7 T data and 0.65 s⁻¹ for 7 T data). Error bars represent the SEM of only the VO animals. The * indicate a significant (p<0.05) difference from control values; the # indicates a significant (p<0.05) difference from the values at 14/0.

Figure 3

Summary of visual performance in variable oxygen exposed Long Evans rats. A: Spatial frequency threshold in control (con) and variable oxygen (VO) rats. The numbers above the bars represent the number of animals in each group. Error bars represent the standard error of the mean (SEM). The * indicates a significant (p<0.05) difference from control values. B: Contrast sensitivity in same two groups as A; circle=con, triangle=VO. These two curves are significantly different (ANOVA, p<0.05).

Figure 4

Summary of the severity retinal neovascularization (NV) severity in untreated variable oxygen (VO) Long Evans rats (VO), VO LE rats treated with diltiazem treatment (DIL) between 14/0 and 14/6 (VO+DIL), and VO LE rats treated with DIL+nifedipine (NIF) between 7/0 and 14/6 (VO+DIL+NIF). The * indicates a significant (p<0.05) difference from values in the VO group. Error bars represent standard error of the mean (SEM), and numbers above the bars represent the number of animals studied.