Localization of mRNAs encoding Ca2+-inhibitable adenylyl cyclases along the renal tubule - Functional consequences for regulation of the cAMP content

Expression of Ca2+-inhibitable types V and VI adenylyl cyclases was studied by reverse transcription-polymerase chain reaction in rat renal glomeruli and nephron segments isolated by microdissection. Quantitation of each mRNA was achieved using a mutant cRNA which differed from the wild type by substituting two bases to create a new restriction site in the corresponding cDNA. Type VI mRNA was present all along the nephron but was more abundant in distal than in proximal segments. The expression of type V mRNA was restricted to the glomerulus and to the initial portions of the collecting duct. Expression of the Ca2+-insensitive type IV mRNA studied on the same samples was evidenced only in the glomerulus, The functional relevance of the expression of Ca2+-inhibitable isoforms was studied by measuring cAMP content in the microdissected enter medullary collecting duct which expressed both type V mRNA (2367 +/- 178 molecules/mm tubular length; n = 8) and type VI mRNA (5658 +/- 543 molecules/mm, n = 8). Agents known to increase intracellular Ca2+ in this segment induced a Ca2+-dependent inhibition on either arginine vasopressin- or glucagon-stimulated cAMP level. The characteristics of these inhibitions suggest a functional and differential expression of types V and VI adenylyl cyclases in two different cell types of the rat outer medullary collecting duct.