MESSENGER-RNAS CODING FOR THE CALCIUM-SENSING RECEPTOR ALONG THE RAT NEPHRON - EFFECT OF A LOW-PHOSPHATE DIET

We investigated the localization of mRNA encoding the calcium-sensing receptor (CaSR) along the rat nephron. For this purpose, we combined m icrodissection of nephron segments and RT-PCR techniques. The results indicate that mRNA encoding rat CaSR is present in rat glomeruli and d istal segments (medullary thick ascending limb, cortical thick ascendi ng limb, distal convoluted tubule and cortical collecting duct), where as it was not detected in proximal convoluted tubules or proximal stra ight tubules. We also studied whether the CaSR transcription in kidney cortex was modified in response to low dietary phosphate. No signific ant changes were detected. Given the fact that a low-phosphate diet in creased Ca2+ excretion by more than 50-fold, the results suggest that if the CaSR regulates Ca2+ reabsorption, it does so through receptor o ccupancy by Ca2+ rather than by changes in receptor expression.