With a bang, a new family of potassium channels has exploded into view. Although KCNK channels were discovered only five years ago, they already outnumber other channel types. KCNK channels are easy to identify because of their unique structure--they possess two preforming domains in each subunit. The new channels function in a most remarkable fashion: they are highly regulated, potassium-selective leak channels. Although leak currents are fundamental to the function of nerves and muscles, the molecular basis for this type of conductance had been a mystery. Here we review the discovery of KCNK channels, what has been learned about them and what lies ahead. Even though two-P-domain channels are widespread and essential, they were hidden from sight in plain view--our most basic questions remain to be answered.

In brain and tumor cells, the hexokinase isoforms, HK-I and HK-II, bind to the voltage-dependent anion channel (VDAC) in the outer mitochondrial membrane. The VDAC domains interacting with these anti-apoptotic proteins were recently defined using site-directed mutagenesis. Now, we demonstrate that synthetic peptides corresponding to the VDAC1 N-terminal region and selected sequences bound specifically, in a concentrationand time-dependent manner, to immobilized HK-I, as revealed by real time surface plasmon resonance technology. The same VDAC1-based peptides also detached HK bound to brain or tumor-derived mitochondria. Moreover, expression of the VDAC1-based peptides in cells overexpressing HK-I or HK-II prevented HK-mediated protection against staurosporine-induced release of cytochrome c and subsequent cell death. One loop-shaped VDAC1-based peptide corresponding to a selected sequence and fused to a cell-penetrating peptide entered the cell and prevented the anti-apoptotic effects of HK-I and HK-II. This peptide detached mitochondrial-bound HK better than did the same peptide in its linear form. Both cell-expressed and exogenously added cell-penetrating peptide detached mitochondrial-bound HK-I-GFP. These results point to HK-I and HK-II as promoting tumor cell survival through binding to VDAC1, thereby inhibiting cytochrome c release and apoptotic cell death. Moreover, VDAC1-based peptides interfering with HK-mediated anti-apoptotic activity may potentiate the efficacy of conventional chemotherapeutic agents.Cancer cells are characterized by a high rate of glycolysis that serves as their primary energy-generating pathway (1). The molecular basis of this high rate of glycolysis involves a number of genetic and biochemical events, including overexpression of the mitochondria-bound hexokinase isoforms, HK-I 2 and HK-II (1-5). In mammals, HK-I and HK-II are strategically located at the outer membrane of mitochondria, where they gain preferential access to mitochondrially generated ATP (6). In this manner, HK-I and HK-II drive the high glycolytic rates typical of tumor cells, even under aerobic conditions (1, 3). Such elevated levels of mitochondria-bound HK is suggested to play a pivotal role in promoting cell growth and survival in rapidly growing, highly glycolytic tumors and in protecting against mitochondria-mediated cell death (1, 4, 7). The elevated levels of HK-I and HK-II allow tumor cells to evade apoptosis, thereby allowing proliferation to continue (4). Indeed, overexpression of mitochondria-bound HK in the tumor-derived cell line U-937, in T-REx-293, or in vascular smooth muscle cells suppressed staurosporine-induced apoptotic cell death (8, 9). A decrease in apoptotic cell death and concomitant increase in cell proliferation have also been reported to be induced upon HK-II expression in NIH-3T3 (7), rat 1a fibroblasts (10), and WEHI 7.1 cells (11). In addition, binding of HK-II to mitochondria inhibited Bax-induced cytochrome c release and apoptosis (12).Mitochondria-mediated apoptosis results in th...

␣-Neurotoxins from scorpion venoms constitute the most studied group of modifiers of the voltage-sensitive sodium channels, and yet, their toxic site has not been characterized. We used an efficient bacterial expression system for modifying specific amino acid residues of the highly insecticidal ␣-neurotoxin Lqh␣IT from the scorpion Leiurus quinquestriatus hebraeus. Toxin variants modified at tight turns, the C-terminal region, and other structurally related regions were subjected to neuropharmacological and structural analyses. This approach highlighted both aromatic (Tyr 10 and Phe 17 ) and positively charged (Lys 8 , Arg 18 , Lys 62 , and Arg 64 ) residues that (i) may interact directly with putative recognition points at the receptor site on the sodium channel; (ii) are important for the spatial arrangement of the toxin polypeptide; and (iii) contribute to the formation of an electrostatic potential that may be involved in biorecognition of the receptor site. The latter was supported by a suppressor mutation (E15A) that restored a detrimental effect caused by a K8D substitution. The feasibility of producing anti-insect scorpion neurotoxins with augmented toxicity was demonstrated by the substitution of the C-terminal arginine with histidine. Altogether, the present study provides for the first time an insight into the putative toxic surface of a scorpion neurotoxin affecting sodium channel gating.

Potassium leak channels are essential to neurophysiological function. Leaks suppress excitability through maintenance of resting membrane potential below the threshold for action potential firing. Conversely, voltage-dependent potassium channels permit excitation because they do not interfere with rise to threshold, and they actively promote recovery and rapid re-firing. Previously attributed to distinct transport pathways, we demonstrate here that phosphorylation of single, native hippocampal and cloned KCNK2 potassium channels produces reversible interconversion between leak and voltage-dependent phenotypes. The findings reveal a pathway for dynamic regulation of excitability.

We describe a maternally transmitted genomic-imprinting syndrome of mental retardation, hypotonia, and unique dysmorphism with elongated face. We mapped the disease-associated locus to approximately 7.27 Mb on chromosome 8q24 and demonstrated that the disease is caused by a missense mutation in the maternal copy of KCNK9 within this locus. KCNK9 is maternally transmitted (imprinted with paternal silencing) and encodes K(2P)9.1, a member of the two pore-domain potassium channel (K(2P)) subfamily. The mutation fully abolishes the channel's currents--both when functioning as a homodimer or as a heterodimer with K(2P)3.1.