Sensitivity of Ca receptor

[pezzang]

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In Qbank, there was a question about a treatment of secondary hyperparathyroidism due to end stage renal failure. The q&a says that cinacalcet is a drug that increases the sensitivity of calcium-sensing receptors to extracellular ionized calcium. If cinacalcet mimics the function of Ca to make the Ca receptor on parathyroid hormone less responsive to Ca, shouldn't it essentially make Ca receptor LESS sensitive to extracellular Ca, not more sensitive?

 

[Ty Webb]

In Qbank, there was a question about a treatment of secondary hyperparathyroidism due to end stage renal failure. The q&a says that cinacalcet is a drug that increases the sensitivity of calcium-sensing receptors to extracellular ionized calcium. If cinacalcet mimics the function of Ca to make the Ca receptor on parathyroid hormone less responsive to Ca, shouldn't it essentially make Ca receptor LESS sensitive to extracellular Ca, not more sensitive?

It's an allosteric modulator (activator) of the calcium-sensing receptor. It therefore makes the Ca-R more prone to activation by Ca2+. It doesn't make it less sensitive to Ca2+, as you were thinking, but rather moreso.

I'm not sure where the confusion is regarding this question. If it's the -mimetic terminology, remember that this doesn't necessarily mean that the drug has the same MOA as the endogenous molecule its "mimicking" (think sympathomimetics, for instance).

Hope this helps.