Expression of mRNAs for different types of IP3 receptors in rat kidneys

Cloning studies have extensively characterized two types of inositol 1,4,5-trisphosphate (IP3) receptors from the rat. An IP3 receptor from the cerebellum is referred to as type 1, and a second, recently described, receptor is referred to as the type 2 IP3 receptor. The significance of different types of IP3 receptors, especially in vivo in the kidney, is not fully understood. We investigated the localization of mRNAs encoding these two types of IP3 receptors in microdissected nephron segments of rats using reverse transcription and polymerase chain reaction (RT-PCR) followed by Southern blot analysis. Type 1 IP3 receptor mRNA displayed a widespread, although not uniform, distribution along the nephron. In contrast, type 2 IP3 receptor mRNA was confined almost exclusively to collecting ducts, suggesting specific expression of type 2 IP3 receptor in collecting ducts. We then detected mRNAs for the two types of IP3 receptors in collecting ducts in dehydrated rats. Dehydration downregulated type 2 IP3 receptor mRNA in cortical collecting duct, outer medullary collecting duct, and the initial part of inner medullary collecting duct (IMCD), but not in the terminal part of IMCD. It had no effect on type 1 IP3 receptor mRNA expression in collecting ducts. We propose that different types of IP3 receptors may have different functions in the rat kidney. the initial part of inner medullary collecting duct (IMCD), but not in the terminal part of IMCD. It had no effect on type 1 IP3 receptor mRNA expression in collecting ducts. We propose that different types of IP3 receptors may have different functions in the rat kidney.