PTH acts on renal tubular cells through a single receptor species that generates two distinct intracellular signals. This receptor achieves dual signalling by simultaneously coupling to:

• A Gs only, with cross-talk generating the calcium signal
• B Gi and Gq, lowering cAMP while raising calcium
• C Gs (raising cAMP) and Gq (raising IP3 and calcium) ✓
• D An intrinsic tyrosine kinase domain and JAK2

Explanation

The PTH/PTHrP receptor (PTH1R) is a promiscuous GPCR that couples to both Gs and Gq. Through Gs it raises cAMP and activates PKA, producing phosphaturia and stimulating 1-alpha hydroxylase. Through Gq it activates phospholipase B, generating IP3 and DAG and raising cytosolic calcium. Loss-of-function mutations produce pseudohypoparathyroidism, whereas gain-of-function mutations cause Jansen metaphyseal chondrodysplasia. No other listed pairing reproduces both limbs of the physiological response.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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