You are studying two identical rhabdomeric photoreceptors, X and Y, and measure

Question

You are studying two identical rhabdomeric photoreceptors, X and Y, and measure
the amount of neurotransmitter released by each photoreceptor at rest. You treat only
Y with 3-nitrocoumarin, a molecule that completely inhibits Phospholipase C. Then
you expose each photoreceptor to an identical light stimulus (of maximal intensity)
and measure the amount of neurotransmitter released while the photoreceptors are
exposed to this stimulus.
a) How much neurotransmitter would you expect X to release at rest? How would this
compare to the amount of neurotransmitter released by a ciliary photoreceptor at rest? (2
marks)
b) When exposed to light, will X and Y both release neurotransmitter? Explain why or why
not. (6 marks)

Explanation / Answer

a). Rhabdomeric photoreceptors depolarize the light and they use phospholipase C. While the ciliary photoreceptors hyperpolarize the light. So, at rest, the neurotransmitter released by ciliary photoreceptors are high and the rhabdomeric receptors is low (because they are activated upon light stimulus).

b). When exposed to light, only X will release neurotransmitter because Y is treated with 3-nitrocoumarin which inhibits the phospholipase C (secondary messenger needed for signal transduction).

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