Department of Integrative Biology and Physiology, University of California, Los Angeles, CA 90095-7239.
Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, CA 90095-7000.
Proc Natl Acad Sci U S A. 2020 Aug 11;117(32):19599-19603. doi: 10.1073/pnas.2001776117. Epub 2020 Jul 27.
We have used recent measurements of mammalian cone light responses and voltage-gated currents to calculate cone ATP utilization and compare it to that of rods. The largest expenditure of ATP results from ion transport, particularly from removal of Na entering outer segment light-dependent channels and inner segment hyperpolarization-activated cyclic nucleotide-gated channels, and from ATP-dependent pumping of Ca entering voltage-gated channels at the synaptic terminal. Single cones expend nearly twice as much energy as single rods in darkness, largely because they make more synapses with second-order retinal cells and thus must extrude more Ca In daylight, cone ATP utilization per cell remains high because cones never remain saturated and must continue to export Na and synaptic Ca even in bright illumination. In mouse and human retina, rods greatly outnumber cones and consume more energy overall even in background light. In primates, however, the high density of cones in the fovea produces a pronounced peak of ATP utilization, which becomes particularly prominent in daylight and may make this part of the retina especially sensitive to changes in energy availability.
我们利用最近对哺乳动物视锥光反应和电压门控电流的测量，计算了视锥细胞的 ATP 利用情况，并将其与视杆细胞进行了比较。ATP 的最大消耗来自离子转运，特别是从外段光依赖通道和内段超极化激活环核苷酸门控通道进入的 Na 的去除，以及从电压门控通道进入突触末端的 Ca 的 ATP 依赖性泵出。在黑暗中，单个视锥细胞的能量消耗几乎是单个视杆细胞的两倍，这主要是因为它们与二级视网膜细胞形成更多的突触，因此必须排出更多的 Ca。在白天，每个细胞的视锥细胞 ATP 利用率仍然很高，因为视锥细胞永远不会饱和，即使在明亮的光照下也必须继续输出 Na 和突触 Ca。在小鼠和人眼中，视杆细胞的数量远远超过视锥细胞，即使在背景光下，它们也消耗更多的能量。然而，在灵长类动物中，中央凹处视锥细胞的高密度产生了明显的 ATP 利用峰值，这在白天尤为明显，可能使视网膜的这一部分对能量供应的变化特别敏感。
