THE ONTOGENY OF THE EXPRESSION OF K-LIKE GENE (CHIF) IN THE RAT-KIDNEY PAPILLA( CHANNEL)

Recently, an IsK-like potassium (K+) channel corticosteroid-induced ge ne (CHIF) was cloned. A high-K+ diet enhances, while a low-Kf diet dec reases the expression of this gene. The major expression of CHIF in th e adult rat kidney is in the papilla, where it is constitutive, in con trast to its inducibility by corticosteroids and a low-salt diet in th e rat colon. In order to further understand the ontogeny of Kf clearan ce, we studied the presence of CHIF in the kidney papilla in different stages of rat development. Total RNA from rat kidney papillae of 1- t o 3-day pre-labor unborn offspring, 2- to 3-day-old newborns, 10-day-o ld, 6-week-old, and 43-week-old rats underwent northern hybridization for CHIF and the alpha-subunit of the Na+-K+-ATPase mRNA. Minor expres sion of CHIF mRNA was found in fetal and newborn rat papillae, while o lder rats showed an age-related increase in gene expression(1). The ex pression of the a-sub unit of the Na+-K+-ATPase was not age related. W e conclude that CHIF is present in the rat kidney papilla and the expr ession is related to age. The relative deficiency of CHIF in the newbo rn may be one of the factors responsible for the reduced K+ clearance in is period.