Background: To determine if the L-type calcium channel participates in the generation of the light-rise of the electro-oculogram (EOG) in man. The aim was to use nifedipine, a specific, L-type calcium channel inhibitor and determine the effects on the light-rise of the EOG in healthy participants.
Methods: The EOG was recorded in 14 participants before and after a 10 mg oral dose of fast-acting nifedipine. The Arden index, time to peak of the EOGs and pulse were recorded before and after ingestion of nifedipine. The test-retest variability of the EOG's light-rise in the absence of nifedipine was performed on 11 of the participants. The mean ± SEM oral dose was 147 ± 9 μg/kg. Scotopic electroretinograms (ERGs) were recorded at four intensities (0.0067, 0.0849, 0.364 and 1.140 cd.s.m⁻²) in six participants before and after a 10 mg oral dose of nifedipine.
Results: The light-rise of the EOG was significantly reduced in five participants by -22.80 ± 5.6% (p = 0.021), whilst in four of the participants the light-rise increased by +15.7 ± 1.9% (p = 0.033). The results of the test-retest EOGs showed a range of -9.1 to +9.8% Arden index in the absence of nifedipine. Thus, the responses of five participants were not included in the analysis, as the change in the EOG with nifedipine was within this range. The differences in the time to peak of the light-rise were not significantly different in those that showed an increase (p = 0.33) or a decrease (p = 0.87) in the EOG after nifedipine. Pulse rate was not significantly different after nifedipine in the group that showed an increased light-rise (p = 0.77) or in those whose light-rise fell after nifedipine (p = 0.33). No significant effect was observed on the a- and b-wave amplitudes and implicit times for the scotopic components of the scotopic ERG.
Conclusions: The L-type calcium channel contributes to the light-rise of the EOG in man.