Dietary K regulates ROMK channels in connecting tubule and cortical collecting duct of rat kidney

Frindt G, Shah A, Edvinsson J, Palmer LG. Dietary K regulates ROMK channels in connecting tubule and cortical collecting duct of rat kidney. Am J Physiol Renal Physiol 296: F347-F354, 2009. First published November 26, 2008; doi:10.1152/ajprenal.90527.2008.-The activity of ROMK channels in rat kidney tubule cells was assessed as tertiapin-Q (TPNQ)-sensitive current under whole cell clamp conditions. With an external K+ concentration of 5 mM and an internal K+ concentration of 140 mM and the membrane potential clamped to 0 mV, TPNQ blocked outward currents in principal cells of the cortical collecting duct (CCD) outer medullary collecting duct and connecting tubule (CNT). The apparent K-i was 5.0 nM, consistent with its interaction with ROMK. The TPNQ-sensitive current reversed at voltages close to the equilibrium potential for K+. The currents were reduced when the pipette solution contained ATP. In the CCD, the average TPNQ-sensitive outward current (I-SK) was 476 +/- 48 pA/cell in control animals on a 1% KC1 diet. I-SK increased to 1,255 +/- 140 pA when animals were maintained on a high-K (10% KC1) diet for 7 days and decreased to 314 +/- 46 pA after 7 days on a low-K (0.1% KC1) diet. In the CNT, I-SK was 360 +/- 30 pA on control, 1,160 +/- 110 on high-K, and 166 +/- 16 pA on low-K diets. The results indicate that ROMK channel activity is highly regulated by dietary K in both the CCD and the CNT.