Which description of opsin–effect pairing is most accurate for bidirectional optogenetic control of neurons?

Question

BlackTom AI · Accepted Answer

To evaluate bidirectional optogenetic control, we need to match each protein's known action on neuronal membranes.
Option 1: 'ChR2 permits depolarizing mixed-cation currents; halorhodopsin pumps chloride to hyperpolarize membranes' This description aligns with the classic pair used for bidirectional control: channelrhodopsin-2 (ChR2) conducts cations (Na+, Ca2+, K+) and causes depolarization when illuminated, while halorhodopsin pumps Cl- ions into the cell to hyperpolarize and inhibit activity. This pairing enables precise excitation and inhibition with light.
Option 2: 'ChR2 pumps chloride to hyperpolarize; halorhodopsin opens nonselective cation channels to depolarize' This reverses the canonical functions. ChR2 is a non-selective cation channel—its primary effect is depolarization via cation influx, not chloride pumping, so describing it as chloride-pumping is incorrect. Halorhodopsin does not open nonselective cation channels to depolarize; it functions as a chloride pump to hyperpolarize, not as a depolarizing channel.
Option 3: 'Melanopsin directly forms an ion channel producing fast depolarization without second messenger signaling' Melanopsin is a G-protein-coupled receptor that signals through second messengers and does not form a direct light-gated ion channel. Its activation involves intracellular cascades, leading to slower responses rather than the fast, direct cation channel activity characteristic of ChR2. Therefore, this option describes a mechanism inconsistent with the optogenetic tools used for rapid bidirectional control.
Overall, the first option correctly assigns ChR2 to depolarizing cation currents and halorhodopsin to chloride pumping for hyperpolarization, while the other options misstate the fundamental mechanisms of these two opsins and melanopsin.

Which description of opsin–effect pairing is most accurate for bidirectional optogenetic control of neurons?Single choice

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