The metabolic syndrome affects 50 million Americans, and is associated with obesity and insulin resistance. Hyperkalemia is associated with life-threatening cardiac arrhythmias and increased mortality, and patients with insulin resistance and Type 2 diabetes are susceptible to hyperkalemia. However, potential derangements in renal potassium (K) handling remain unexplored. As part of our ongoing NIH-sponsored studies of ion channel function in insulin resistance, we, the Investigators (PI and Co-I), uncovered that flow-induced K secretion (FIKS) in the distal nephron, mediated by BK channels, and renal K handling is defective. Deletion of BK channels leads to defective renal K handling, and impaired K adaptation. The objective of this proposal is to determine the mechanisms underlying the reduction in BK channel- mediated FIKS in the distal nephron and to determine the consequences for K adaptation and hyperkalemia in the insulin resistance syndrome. The R01 Grant will provide the necessary resources to test the hypothesis that insulin resistance in the distal nephron is a phenocopy for BK channel deficiency with decreased insulin signaling leading to disrupted BK channel activity, and thus, defective FIKS and K adaptation, and predisposition to hyperkalemia. To test this hypothesis, we propose two specific aims.
Aim #1 is to determine the cellular mechanisms of distal nephron BK channel dysfunction in a mouse model of insulin resistance. Using control and insulin resistant mice, we will measure expression and subcellular localization of distal nephron BK and Ca2+- channels using two innovative methodologies, and will study the Ca2+ and voltage sensitivity of BK channels. We will also measure the impact of defective BK channels on K adaptation and hyperkalemia in the metabolic syndrome.
Aim #2 is to determine whether impaired insulin receptor signaling in the distal nephron is sufficient to phenocopy the BK channel dysfunction of insulin resistance. Using a novel renal tubular insulin receptor knockout mouse, we will measure BK and Ca2+ channel expression, and subcellular localization using similar methods to Aim #1. We will study the Ca2+ and voltage sensitivity of BK channels in control and knockout mice and will measure the effect of deletion of insulin receptor signaling on K adaptation and hyperkalemia. We will also measure cell signaling pathways related to insulin and BK channels. We anticipate that these results will significantly advance the field by identifying appropriate dietary and pharmaceutical targets for the prevention and treatment of hyperkalemia in diseases associated with insulin resistance, such as obesity and Type 2 diabetes mellitus. The proposed research is innovative in that we will directly study the regulation of renal BK channels in insulin resistance and will employ novel reagents and cutting-edge techniques to understand the consequences of defective FIKS for hyperkalemia. Through the proposed studies, we will also learn about mechanisms of insulin signaling in the kidney in the insulin resistance syndrome and the role of diet in determining cardiovascular outcomes in this syndrome.
As the incidence of insulin resistance increases in the general population, so will the consequences of this syndrome. Using mouse models of insulin resistance, we have uncovered that the way the kidney collecting duct handles potassium is defective which may place individuals with insulin resistance at risk for high levels of blood potassium and life-threatening arrhythmias. For the proposed studies we will study the mechanisms and consequences of this defective potassium handling by the kidney in order to identify targeted dietary and pharmacologic therapies for insulin resistance to alleviate the burdens of hyperkalemia and cardiovascular disease in this subset of patients.