QUANTITATIVE RT-PCR ANALYSIS OF CALCITONIN RECEPTOR MESSENGER-RNAS INTHE RAT NEPHRON

A quantitative assay based on the method of reverse transcription and polymerase chain reaction (RT-PCR) was developed to study the expressi on of calcitonin (CT) receptors in microdissected rat nephron segments . Steady-state mRNA levels of two CT-receptor spliced variants (CT1a a nd CT1b) were measured using a mutant cRNA as internal standard. CT1a, but not the CT1b isoform, was detected in the kidney cortex, outer me dulla, and papilla. Among the tested segments, predominant expression of CT1a mRNA was found in the cortical thick ascending limb of Henle's loop (754 +/- 87 mRNA molecules/mm tubular length; n = 8). Lower expr ession levels were measured in the medullary thick ascending limb (460 +/- 62 molecules/mm tubule length; n = 7) and in the cortical collect ing duct (327 +/- 61 molecules/mm tubule length; n = 6). A weak expres sion was also detected in the outer medullary collecting duct and the glomerulus. No expression was found in the proximal convoluted tubule, pars recta, and thin descending and thin ascending limb of Henle's lo op. We conclude that only the CT1a-receptor mRNA is present in the rat kidney, with a significant level of expression in the cortical and me dullary thick ascending limb and in the cortical collecting duct.