Voltage-gated potassium channels (Kv) maintain the resting membrane potential and the shape of the action potential. The activity of these channels modulates cardiac pacemaking, the action potential duration and neurotransmitter release. In addition, these channels play an important role in oxygen-sensing, cell-volume regulation, and apoptosis. The ion-conducting pore of these channels is formed by homomeric or heteromeric assembly of Kv proteins. The cytoplasmic domain of several Kv proteins interacts with ancillary 2-subunits that belong to the aldo-keto reductase (AKR) superfamily. The Kv2 proteins display high affinity pyridine nucleotide binding and catalyze aldehyde reduction. The general physiological role of Kv2, however, remains unclear and the contribution of the AKR properties of Kv2 to the regulation of Kv channel activity has not been assessed. We propose that the binding of pyridine nucleotides to the AKR domain of the 2-subunit imparts metabolic sensitivity to Kv channels, such that an increase in the NAD(P)H/NAD(P)+ ratio increases Kv inactivation; thus coupling Kv channel activity to the metabolic state of the heart. Because the ratio of reduced and oxidized nucleotides is tightly controlled by glycolysis and mitochondrial respiration, we suggest that differential regulation of Kv1-2 currents by pyridine nucleotides is a physiological mechanism that couples myocardial excitation to changes in intermediary metabolism during hypoxia, ischemia, and apoptosis. To test this hypothesis, we will (S.
Aim 1) delineate the contribution of pyridine nucleotides to the regulation of Kv currents by Kv2; (S.
Aim 2) examine the metabolic dependence of Kv2-induced-inactivation of Kv currents; and (S.
Aim 3) elucidate the role of Kv2 in regulating native Kv channels in the heart. To assess the significance of nucleotide binding at the aldo-keto reductase domain of Kv2 proteins, we will determine how changes in the redox state of pyridine nucleotides or the nucleotide binding affinity, induced by site-directed mutagenesis, affects the ability of Kv22 to interact with or alter Kv1.5 currents. To examine the metabolic-dependence of Kv2-inactivation of Kv currents, we will investigate how changes in metabolism or oxygen concentration affect Kv1-2 currents. For this, we will measure Kv currents from cells subjected to hypoxia or treated with metabolic inhibitors and determine whether differential pyridine nucleotide binding to Kv2 is essential for imparting metabolic and oxygen sensitivity to Kv1.5 currents. To determine how the redox properties of Kv2 affect the pathophysiological responses of Kv channels, we will examine how metabolic inhibitors or components of ischemia affect Kv currents in cardiac myocytes isolated from wild-type, Kv2-null and Kv22:Y90F mice, and whether loss of Kv2 affects tissue injury and dysfunction due to acute myocardial infarction. Successful completion of this study will provide insights in to the Kv channel function and how these channels respond to changes in myocardial oxgyen levels and metabolism. These findings could provide insights into the development of new therapeutic interventions for the treatment and management of myocardial ischemic injury.
Heart attack is a major cause of death in US. Patients with heart disease or loss of blood supply to the heart leads to cell death and arrhythmia of the heart. Ion channels in the heart maintain the normal rhythmic beating and pumping function. However, dysregulation in the ion channel activity can cause abnormal beating and death. The underlying causes for this are unknown. The present study addresses this important aspect of ion channels of the heart, in particular the potassium channel and its regulatory function in sensing the metabolic state of the heart. The voltage-gated potassium channel (Kv channel) in the heart is mainly composed of the transmembrane alpha subunit (Kv channel) and the auxiliary beta-subunits that bind the Kv channel from the cytosolic side and modulate their properties. Loss of blood flow to the heart leads to decrease oxygen supply and energy crisis, this metabolically altered state causes disruption of normal biological pathways inside the heart cell and accumulate chemicals and byproducts. We specifically ask if the potassium channels along with its auxiliary subunit are able to sense the metabolic changes. Therefore establishing the sensory role of the voltage-gated potassium channels can improve our fundamental knowledge about the regulator role of these channel and its subunits. Because such responses are key aspects of Kv activity in cardiac as well as non- cardiac tissues our results may be of significance in understanding how these channels regulate pulmonary arteries, brain and how they participate in a host of diverse functions such as oxygen-sensing, cell growth, apoptosis.
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