A drug inhibitor of cyclic GMP phosphodiestera... in rod photoreceptors?

Question

The rod photoreptors in the eye are extremly sensitive to light. Rod cells sense light through a signal transduction cascade involving light-activation of a G-protein linked receptor that activates a g-protein, which activates cyclic GMP phosphodiesterase. How would I expect the addition of a drug that is an inhibitor of Cyclic GMP photodiesterase and a drug that is a non-hydrolyzable analog of GTP to affect in the rod cells? Please site your sources if you have any thanks

Answer 1

Welcome back to biology...

In order to complete the cascade you have to consider that cGMP keeps some cation specific channels open. Hydrolysis of cGMP leads to closed channels, hyperpolarization of the plasma membrane which is transmitted to the synaptic body.
So if you put an inhibitor of the enzyme, there will be no cGMP hydrolysis, thus the channels will remain open, there will be no hyperpolariztion and thus no signal to the nerve.

cGMP phosphodiesterase (PDE) is activated when the complex of the a subunit of transducin and GTP (Ta-GTP)binds to the PDE and relieves the inhibitory effect of the γ subunit of PDE.
So if you put a GTP analogue that cannot be hydrolysed then PDE will be always active (inactivation occurs by the hydrolysis of GTP in the Ta-GTP complex).
If you had enough cGMP formed before applying the drug, then you will have cGMP continuously hydrolysed, the channels always closed, hyperpolarization and continuous signaling.
The cell would not be able to recover completely since it will not be able to restore cGMP levels (on one hand the analogue of GTP cannot be used for cGMP synthesis and on the other you have constant PDE activity).
If cGMP levels were low to begin with then the system will not be able to recover to the original state (no further cGMP synthesis, thus channels closed) and will keep giving a constant signal to the nerve.

Sorry for mixing up things in the answer in the other category

Answer 2

woman do your homework on your own! =P

Ok check this out, no sources to list now, but from my studies. There is a chemical pathway for that GTP to phosphorylate to GDP or GMP, yes? In that cycle - i forgot the name - there are certain inhibitor proteins. Certain drugs act similar to these proteins and inhibit the cycle. You find out what that drug is through experimentation, and get back to the world with your fascinating research. Then you can get your phd and get pizaid!