Regulation of potassium channel Kir 1.1 (ROMK) abundance in the thick ascending limb of Henle's loop

The renal outer medullary potassium channel (ROMK) of the thick ascending l imb (TAL) is a critical component of the counter-current multiplication mec hanism. In this study, two new antibodies raised to ROMK were used to inves tigate changes in the renal abundance of ROMK with treatments known to stro ngly promote TAL function. These antibodies specifically recognized protein of the predicted size of 45 kD in immunoblots of rat kidney or COS cells t ransfected with ROMK cDNA. Infusion of 1-deamino-(8-D-arginine)-vasopressin (dDAVP), a vasopressin V2 receptor-selective agonist, for 7 d into Brattle boro rats resulted in dramatic increases in apical membrane labeling of ROM K in the TAL of dDAVP-treated rats, as assessed by immunocytochemical analy ses. Using immunoblotting, a more than threefold increase in immunoreactive ROMK levels was observed in the outer medulla after dDAVP infusion. Restri ction of water intake to increase vasopressin levels also significantly inc reased TAL ROMK immunolabeling and abundance in immunoblots. In addition, d ietary Na+ levels were varied to determine whether ROMK abundance was also affected under other conditions known to alter TAL transport. Rats fed high er levels of sodium, as either NaCl or NaHCO3 (8 mEq/250 g body wt per d), exhibited significantly increased density of the 45-kD band, compared with the respective control animals. Moreover, in rats fed a low-NaCl diet (0.25 mEq/250 g body wt per d), a 50% decrease in band density for the 45-kD ban d was observed (relative to control rats fed 2.75 mEq/250 g body wt per d o f NaCl). These results demonstrate that long-term adaptive changes in ROMK abundance occur in the TAL with stimuli that enhance transport by this segm ent.