The activity of the epithelial Na+ channel (ENaC) in principal cells of the aldosterone-sensitive distal nephron is central to renal salt and water handling, and thus, regulation of blood pressure. Indeed, gain and loss of ENaC function causes marked increases and decreases in blood pressure. Negative-feedback regulation of ENaC by the renin-angiotensin-aldosterone system (RAAS) is well described where changes in blood pressure ultimately affect ENaC activity in the kidney. Emerging evidence suggests that ENaC is also under feedback control by signaling intrinsic to the kidney mediated by local factors. However, compared to extrinsic regulation by RAAS, less is known about intrinsic control. Purinergic signaling factors are leading candidates as autocrine/paracrine factors important to distal nephron Na+ transport. Our overarching idea is that distal nephron salt and water handling is influenced by intrinsic systems to lessen distal compensation of proximal events enabling excretion to appropriately match systemic conditions. Loss of such intrinsic regulation is expected to cause or exacerbate improper renal Na+ retention and thus, hypertension. It is striking that mice engineered to lack purinergic P2Y2 receptors or connexin 30 hemi-channels, which likely are responsible, in part, for ATP release in the distal nephron, have hypertension associated with facilitated renal Na+ retention. In consideration of our strong preliminary results, we test our central hypothesis that physiological down- regulation of ENaC activity in response to local ATP signaling in the distal nephron through luminal P2Y2 receptors tempers Na+ reabsorption by addressing four specific aims: 1) determine whether physiological concentrations of ATP affect ENaC activity in the mammalian distal nephron and determine the cellular signaling pathway and mechanism of action;2) determine the consequence of dysfunctional regulation of ENaC by compromised paracrine/autocrine ATP signaling;3) define the role of connexin 30 in ATP regulation of ENaC;and 4) quantify the relation between systemic salt-loading and regulation of ENaC activity in the distal nephron by purinergic tone. We investigate purinergic regulation of ENaC using a comprehensive strategy combining direct measurements of channel activity with electrophysiology with a molecular genetics approach that unequivocally establishes the role of the P2Y2 receptor and probes Cx30 as a conduit for autocrine ATP release. Physiologically relevant tissue (freshly isolated murine collecting duct) containing native ENaC in its normal cellular environment is used. Moreover, the scope of this proposal is comprehensive probing regulation of ENaC by purinergic tone and ATP release via Cx30 in the collecting duct from the animal to molecular mechanism of action.
Hypertension is prevalent in America and continues to rise making it one of the major obstacles for better quality of life and health care in the U.S. A. Appropriate salt handling by the kidneys is critical to proper control of blood pressure. The current proposal investigates the cellular and molecular mechanisms underlying renal salt handling particularly at the distal nephron, the location where systemic salt and water balance is fine-tuned in humans.
|Mironova, Elena; Bugay, Vladislav; Pochynyuk, Oleh et al. (2013) Recording ion channels in isolated, split-opened tubules. Methods Mol Biol 998:341-53|
|Toney, Glenn M; Vallon, Volker; Stockand, James D (2012) Intrinsic control of sodium excretion in the distal nephron by inhibitory purinergic regulation of the epithelial Na(+) channel. Curr Opin Nephrol Hypertens 21:52-60|