Activation of Phospholipase C Mimics the Phase Shifting Effects of Light on Melatonin Rhythms in Retinal Photoreceptors

Abstract

Many aspects of retinal photoreceptor function and physiology are regulated by the circadian clocks in these cells. It is well established that light is the primary stimulus that entrains these clocks; yet, the biochemical cascade(s) mediating light’s effects on these clocks remains unknown. This deficiency represents a significant gap in our fundamental understanding of photoreceptor signaling cascades and their functions. In this study, we utilized re-aggregated spheroid cultures prepared from embryonic chick retina to determine if activation of phospholipase C in photoreceptors in the absence of light can phase shift the melatonin secretion rhythms of these cells in a manner similar to that induced by light. We show that spheroid cultures rhythmically secrete melatonin and that these melatonin rhythms can be dynamically phase shifted by exposing the cultures to an appropriately timed light pulse. Importantly, we show that activation of phospholipase C using m-3M3FBS in the absence of light induces a phase delay in photoreceptor melatonin rhythms that mirrors that induced by light. The implication of this finding is that the light signaling cascade that entrains photoreceptor melatonin rhythms involves activation of phospholipase C.

Oxaliplatin Causes Transient Changes in TRPM8 Channel Activity

“…While we saw a tendency of decreased TRPM8 activity with the PLC activator alone ( m -3M3FBS 25 µM), we could reproduce the reduction of TRPM8 activity by oxaliplatin (oxaliplatin: p = 0.003; oxaliplatin ±10 µM PLC agonist: p < 0.0001; oxaliplatin ±25 µM PLC agonist: p < 0.0019). Additional treatment with the PLC activator ( m -3M3FBS [ 30 ], 10 µM and 25 µM for 24 h) did not cause additional reduction of TRPM8 activity, indicating that the desensitizing effect of oxaliplatin on TRPM8 activity may already be at maximum and cannot be further potentiated by additional PLC activation ( Figure 3 D,E).…”