Tuning Outer Segment Ca2+Homeostasis to Phototransduction in Rods and Cones

摘要: Cone photoreceptors respond to light with less sensitivity, faster kinetics and adapt over a much wider range of intensities than do rods. These differences can be explained, in part, by the quantitative molecular processes that regulate cytoplasmic free Ca2+concentration outer segment both receptor types. is regulated through kinetic balance between ions’ influx efflux action intracellular buffers. Influx passive mediated cyclic-GMP gated ion channels. In cones, Ca2+ions carry about 35% ionic current flowing channels darkness. rods, contrast, this fraction 20%. We present rate model helps explain their Ca2+fractional flux. but not cGMP-sensitivity cyclic GMP-gated changes Ca2+at concentrations expected dark-adapted photoreceptors. Ca2+efflux active Na+and K+dependent exchanger. The Ca2+clearance exchanger regardless absolute size order tens milliseconds. rod segments, again independently size, hundreds milliseconds seconds. investigate functional consequences these Ca2+homeostasis using computational models phototransduction signal rods cones. Consistent experimental observation, make cone’s flash response sensitive simulations, however, changing sufficient recreate authentic cone responses. Accelerating inactivation (but NOT activation) enzymes transduction cascade, addition, are needed photosignals.