Does melanopsin bistability have physiological consequences?

Recent publications in the Journal of Biological Rhythms have focused on the hypothesis that the property of melanopsin bistability is functionally translated to in vivo mammalian physiology. Physiological consequences of photopigment bistability likely can be inferred from the more extensive invertebrate literature. In invertebrates, photopigment bistability results in (a) photoreceptor independence from specialized chromophore regenerating systems, (b) long-wavelength enhancement of a blue light effect, (c) expression of a prolonged depolarization after potential following intense blue light stimulation,and (d) photopigment endocytosis following chronic short-wavelength light exposure. If analogous physiological phenomena result from melanopsin bistability in mammals, then one can take advantage of the spectral composition of a light source to modulate its impact on photoentrainment and other light-dependent circadian phenomena. In any event,investigators studying phenomena that are affected by photic stimulation of intrinsically photosensitive retinal ganglion cells should detail the spectral composition of their light sources before, during, and after an experimental photic stimulus.