GFP-Margatoxin, a Genetically Encoded Fluorescent Ligand to Probe Affinity of Kv1.3 Channel Blockers.

Peptide pore blockers and their fluorescent derivatives are useful molecular probes to study the structure and functions of the voltage-gated potassium Kv1.3 channel, which is considered as a pharmacological target in the treatment of autoimmune and neurological disorders. We present Kv1.3 fluorescent ligand, GFP-MgTx, constructed on the basis of green fluorescent protein (GFP) and margatoxin (MgTx), the peptide, which is widely used in physiological studies of Kv1.3. Expression of the fluorescent ligand in E. coli cells resulted in correctly folded and functionally active GFP-MgTx with a yield of 30 mg per 1 L of culture. Complex of GFP-MgTx with the Kv1.3 binding site is reported to have the dissociation constant of 11 ± 2 nM. GFP-MgTx as a component of an analytical system based on the hybrid KcsA-Kv1.3 channel is shown to be applicable to recognize Kv1.3 pore blockers of peptide origin and to evaluate their affinities to Kv1.3. GFP-MgTx can be used in screening and pre-selection of Kv1.3 channel blockers as potential drug candidates.

Olfactory bulb-targeted quantum dot (QD) bioconjugate and Kv1.3 blocking peptide improve metabolic health in obese male mice.

The olfactory system is a driver of feeding behavior, whereby olfactory acuity is modulated by the metabolic state of the individual. The excitability of the major output neurons of the olfactory bulb (OB) can be modulated through targeting a voltage-dependent potassium channel, Kv1.3, which responds to changes in metabolic factors such as insulin, glucose, and glucagon-like peptide-1. Because gene-targeted deletion or inhibition of Kv1.3 in the periphery has been found to increase energy metabolism and decrease body weight, we hypothesized that inhibition of Kv1.3 selectively in the OB could enhance excitability of the output neurons to evoke changes in energy homeostasis. We thereby employed metal-histidine coordination to self-assemble the Kv1.3 inhibitor margatoxin (MgTx) to fluorescent quantum dots (QDMgTx) as a means to label cells in vivo and test changes in neuronal excitability and metabolism when delivered to the OB. Using patch-clamp electrophysiology to measure Kv1.3 properties in heterologously expressed cells and native mitral cells in OB slices, we found that QDMgTx had a fast rate of inhibition, but with a reduced IC50, and increased action potential firing frequency. QDMgTx was capable of labeling cloned Kv1.3 channels but was not visible when delivered to native Kv1.3 in the OB. Diet-induced obese mice were observed to reduce body weight and clear glucose more quickly following osmotic mini-pump delivery of QDMgTx/MgTx to the OB, and following MgTx delivery, they increased the use of fats as fuels (reduced respiratory exchange ratio). These results suggest that enhanced excitability of bulbar output neurons can drive metabolic responses.

Differential expression of Kv1.3 and Kv1.5 voltage-dependent K+ channels in human skeletal muscle sarcomas.

Because Kv1.3 and Kv1.5 K(+) channels are remodeled during tumorigenesis and participate in skeletal muscle proliferation, we analyzed their expression in human skeletal muscle sarcomas. Aggressive alveolar rhabdomyosarcoma (ARMS) and embryonal rhabdomyosarcoma (ERMS) were studied. Kv1.5 expression was moderate in adult muscle and low in ERMS, whereas it was notable in ARMS and embryonic samples. Kv1.3 expression showed no major differences between RMS and healthy samples. We found a correlation of Kv1.3 and Kv1.5 expression with the tumor malignancy.

Targeting the voltage-dependent K(+) channels Kv1.3 and Kv1.5 as tumor biomarkers for cancer detection and prevention.

Potassium channels (KCh) are a diverse group of membrane proteins that participate in the control of the membrane potential. More than eighty different KCh genes have been identified, which are expressed in virtually all living cells. In addition to nerve and cardiac action potentials, these proteins are involved in a number of physiological processes, including cell volume regulation, apoptosis, immunomodulation and differentiation. Furthermore, many KCh have been reported to play a role in proliferation and cell cycle progression in mammalian cells, and an important number of studies report the involvement of KCh in cancer progression. The voltage dependent potassium (Kv) channels, in turn, form the largest family of human KCh, which comprises about 40 genes. Because Kv1.3 and Kv1.5 channels modulate proliferation of different mammalian cells, these proteins have been analyzed in a number of tumors and cancer cells. In most cancers, the expression patterns of Kv1.3 and Kv1.5 are remodeled, and in some cases, a correlation has been established between protein abundance and grade of tumor malignancy. The list of cancers evaluated is constantly growing, indicating that these proteins may be future targets for treatment. The aim of this review is to provide an updated overview of Kv1.3 and Kv1.5 channels during cancer development. Unlike Kv1.5, Kv1.3 is characterized by a very selective and potent pharmacology, which could lead to specific pharmacological targeting. Because potassium channels may play a pivotal role in tumor cell proliferation, these proteins should be taken into account when designing new cancer treatment strategies.

Voltage-dependent potassium channels Kv1.3 and Kv1.5 in human fetus.

Voltage-dependent K(+) channels (Kv) control repolarization and membrane potential in electrically excitable cells. In addition, Kv channels are involved in the maintenance of vascular smooth muscle tone, insulin release, epithelial K(+) transport, cell proliferation and leukocyte activation. Kv1.3 and Kv1.5 are widely distributed throughout the body and are involved in a variety of physiological processes taking place in the immune system, brain and muscle. Since the developmental pattern of Kv channels has an essential role in the maturing human, we aimed to study Kv1.3 and Kv1.5 channels in 8-10 week human fetal tissues. We chose that gestational age because all organs are in place and the nervous system, although not fully developed. However, the human embryo is undergoing major changes, which will lead to a defined adult pattern. Our results indicated that numerous tissues expressed Kv1.3 and Kv1.5. While Kv1.3 overlapped with the central and peripheral nervous systems, Kv1.5 was mostly localized in the central nervous system. In addition, both channels were abundantly expressed in the hematopoietic fetal liver. Finally, Kv1.5 heavily stained skeletal muscle and heart, whereas Kv1.3 was slightly present. This is the first study to analyze Kv1.3 and Kv1.5 in human during the beginning of fetal development.

Identification of a voltage-gated potassium channel in gerbil hippocampal mitochondria.

Transient cerebral ischemia is known to induce endogenous mechanisms that can prevent or delay neuronal injury, such as the activation of mitochondrial potassium channels. However, the molecular mechanism of this effect remains unclear. In this study, the single-channel activity was measured using the patch-clamp technique of the mitoplasts isolated from gerbil hippocampus. In 70% of all patches, a potassium-selective current with the properties of a voltage-gated Kv-type potassium channel was recorded with mean conductance 109+/-6pS in a symmetrical solution. The channel was blocked at negative voltages and irreversibly by margatoxin, a specific Kv1.3 channel inhibitor. The ATP/Mg(2+) complex and Ca(2+) ions had no effect on channel activity. Additionally, agitoxin-2, a potent inhibitor of voltage-gated potassium channels, had no effect on mitochondrial channel activity. This observation suggests that in contrast to surface membrane channels, the mitochondrial voltage-gated potassium channel could have a different molecular structure with no affinity to agitoxin-2. Western blots of gerbil hippocampal mitochondria and immunohistochemistry on gerbil brain sections confirmed the expression of the Kv1.3 protein in mitochondria. Our findings indicate that gerbil brain mitochondria contain a voltage-gated potassium channel that can influence the function of mitochondria in physiological and pathological conditions and that has properties similar to the surface membrane Kv1.3 channel.