Molecular of ROMK Channel Function

ROMK (Kir 1.1, the product of the KCNJ1 gene) channels in the distal nephron are exquisitely regulated to adjust renal potassium excretion and maintain potassium balance. Still, the underlying mechanisms have been a great mystery. Here we overcome this major conceptual roadblock, building on our recent discoveries of a mechanism we call the potassium switch. We identified two new elements of the switch pathway that regulate ROMK: structural remodeling of the connecting tubule (CNT), and a plasma potassium sensing signaling pathway in the CNT, composed of Kidney Specific (KS)-WNK1, WNK4, and ERK. To carry these breakthrough observations toward a completely new understanding of how potassium balance is achieved, we will use a stepwise multidisciplinary approach, combining molecular genetics, genomics, cellular biology, innovative imaging, state-of-the-art physiological phenotyping in novel mouse models, and mathematical modeling to: 1) Rigorously explore the physiology of newly developed inducible cell-specific ROMK knockout to determine if the regulated expression of ROMK in DCT2 and CNT controls potassium homeostasis, 2) Investigate the adaptive expansion of the CNT as a normal homeostatic mechanism that preserves potassium balance in the face of increased dietary potassium consumption. 3) Test if switch activation of the cell- fate determinants, Jagged 1-Notch 1/2, are required for proper remodeling of the CNT. 4) Explore a potassium-sensing signaling pathway that downregulates ROMK in potassium deficiency via KS-WNK1/WNK4/ERK5 phosphorylation of the clathrin adaptor, ARH, which targets ROMK for endocytosis. The pathway provides a molecular mechanism to explain how ROMK channels are regulated in hypokalemia and dietary potassium deficiency and pathologically misregulated in a human disease of familial hyperkalemia that is induced by gain-of-function mutations in the kidney-specific WNK1. The studies should provide novel insights into the molecular basis of renal K+ handling and K+ homeostasis in health and disease while illuminating novel drug targets for the treatment of common hyperkalemic disorders.