1. A possible side-effect of some phosphodiesterase (PDE) inhibitors is disturba

Question

1.   A possible side-effect of some phosphodiesterase (PDE) inhibitors is disturbances in vision. Explain how, at the cellular level, a PDE inhibitor might interfere with normal vision

2. Taste buds for sweet flavors have receptors that activate in the presence of sugars. These receptors are G-protein coupled receptors (GPCRs). Given what you know about signal transduction, describe a hypothetical signaling pathway that could explain how sugar binding to a GPCR is transformed into a signal that results in neurotransmitter release.

Explanation / Answer

Answer=

At the cellular level, a PDE inhibitor might interfere with normal vision as follows:

PDE2,PDE5 and PDE9 isoforms are expressed in retinal pigment epithelium (RPE) cells,regulating the intracellular cGMP concentrations.

The cGMP of RPE cells seems to activate the RPE pump,contributing to absorption of subretinal fluid.

Because of the presense of phosphodiesterase 5(PDE5) in choroidal and retinal vessels these medications increase choroidal blood flow and cause vasodilation of the retinal vasculature.

The most common symptoms are a blue tinge to vision and an increased sensitivity to light.

There have been non-arteritic anterior ischaemic optic neuropathy and serous macular detachment in users of PDE5.inhibitors.

it has a role of cGMP production and drainage of aqueous humour

All PDE5 inhibitors weakely inhibit PDE6 located in rod and cone photoreceptors resulting in mild and transient visual symptoms that correlate with plasma concentrations.

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