A circadian clock regulates the pH of the fish retina

1. Although it is generally accepted that the acid/base ratio of tissue, as represented by the pH, is strictly regulated to maintain normal function, recent studies in the nervous system have shown that neuronal activity can result in significant shifts in pH. In the vertebrate retina, many cellular phenomena, including neuronal activity, are regulated by a circadian clock . We thus investigated whether a circadian clock regulates the pH of the re tina. 2. pH-sensitive microelectrodes were used to measure the extracellular pH o f the in vitro goldfish retina superfused with a bicarbonate-based Ringer s olution in the subjective day and night; that is, under conditions of const ant darkness. 3. These measurements demonstrated that a circadian clock regulates the pH of the vertebrate retina so that the pH is lower at night compared to the d ay. This day-night difference in retinal pH was observed at two different v alues of Ringer solution pH, indicating that the circadian phenomenon is in dependent of the superfusion conditions. 4. The circadian-induced shift in pH was several times greater than light-i nduced pH changes and large enough to influence synaptic transmission betwe en retinal neurons. 5. These findings indicate that a circadian clock regulates the pH of the v ertebrate retina. Thus, an intrinsic oscillator in neural tissue may modula te metabolic activity and pH as part of normal daily function.