【多选题】How does the light-induced signaling cascade in rod photoreceptor cells greatly amplify the light signal?
A.
When rod photoreceptors are adapted for dim light, the signal amplification is enormous. The cascade functions as follows. In the absence of a light signal, the second messenger molecule cyclic GMP is continuously produced by guanylyl cyclase in the cytosol of the photoreceptor cell.
B.
The cyclic GMP then binds to cation channels in the photoreceptor cell plasma membrane, keeping them open. Activation of rhodopsin by light results in the activation of transducin α subunits.
C.
These turn on an enzyme called cyclic GMP phosphodiesterase, which breaks down cyclic GMP to GMP (much as cyclic AMP phosphodiesterase breaks down cyclic AMP). The sharp fall in the cytosolic concentration of cyclic GMP reduces the amount of cyclic GMP bound to the cation channels, which therefore close.
D.
Closing these channels decreases the influx of Na + , thereby altering the voltage gradient (membrane potential) across the plasma membrane and, ultimately, the rate of neurotransmitter release .