LOCALIZATION OF MESSENGER-RNAS 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 st udied by reverse transcription-polymerase chain reaction in rat renal glomeruli and nephron segments isolated by microdissection. Quantitati on of each mRNA was achieved using a mutant cRNA which differed from t he wild type by substituting two bases to create a new restriction sit e in the corresponding cDNA. Type VI mRNA was present all along the ne phron but was more abundant in distal than in proximal segments. The e xpression of type V mRNA was restricted to the glomerulus and to the i nitial portions of the collecting duct. Expression of the Ca2+-insensi tive type IV mRNA studied on the same samples was evidenced only in th e glomerulus, The functional relevance of the expression of Ca2+-inhib itable isoforms was studied by measuring cAMP content in the microdiss ected enter medullary collecting duct which expressed both type V mRNA (2367 +/- 178 molecules/mm tubular length; n = 8) and type VI mRNA (5 658 +/- 543 molecules/mm, n = 8). Agents known to increase intracellul ar Ca2+ in this segment induced a Ca2+-dependent inhibition on either arginine vasopressin- or glucagon-stimulated cAMP level. The character istics of these inhibitions suggest a functional and differential expr ession of types V and VI adenylyl cyclases in two different cell types of the rat outer medullary collecting duct.