Regulation Of Spectral Sensitivity On Retinal Horizontal Cell & AMPA Triggered Intracellular Calcium Dynamics

The red flickering ind u ced chang e s of R/G HC. s responsiveness and the underlying m echanis m were investigated w ith the intracellular recording. It was found that the red flickering could induce enhancem ent of the depolarizing response of R/G HC t o m oderate red flash and gradua l hyperpolarization of the ce ll. s res ting m e mbrane potential. T h ese ef fects we re blocked by GABA perfusion, which suggested th at the red flickering m i ght in crease the ef ficacy of GABAer gic pathway from HC to cone photorecepto rs and lead to enhancem ent of R/G HC. s red response. It was of particular intere st to note that the activati on of dopam i ner g ic pathway m a y play a crucial role in the process. Destroying the dopa m i ner g ic neuron in retina with 6-OHDA elim inated both ef fects of the red flickering on R/G HC. Further evidence showed that activ ation of D 2 recep tors, probably residing on cone photoreceptor , bu t not D 1 receptor , is necessary . W e hypothesized that red flickering could m odulat e the activity of GABA receptor on co ne phot oreceptor wherein the stim ulation of D 2 recep tor is required. Based on the evidence through electr ophysiological experim e nt and model sim u lation in our lab, the red flickeri ng induced red respons e enhan cem ent of lum i nosity of horizontal cell was supposed to be related to the postsynaptic calcium signal. T o f u rther inv e s tiga t e the p o ssible ca lc ium m echanism , we established the calcium i m a g ing technique on freshly disso ciated horizontal cells and studied the calcium dynam i cs of HC during activa tion of AMP A receptors. The results indicated th at there ex is ted calcium perm eable AMP A receptors on HC and calciu m inf l ux throu gh these re ceptors m a y f u rthe r ind u ce ca lcium rele ase f r o m internal calcium store.