We have investigated the possible implication of the cell cycle-regulated K ⍣ channel ether à go-go (EAG) in cell proliferation and transformation. We show that transfection of EAG into mammalian cells confers a transformed phenotype. In addition, human EAG mRNA is detected in several somatic cancer cell lines, despite being preferentially expressed in brain among normal tissues. Inhibition of EAG expression in several of these cancer cell lines causes a significant reduction of cell proliferation. Moreover, the expression of EAG favours tumour progression when transfected cells are injected into immune-depressed mice. These data provide evidence for the oncogenic potential of EAG.

It is commonly accepted that cells require K(+) channels to proliferate. The role(s) of K(+) channels in the process is, however, poorly understood. Cloning of K(+) channel genes opened the possibility to approach this problem in a way more independent from pharmacological tools. Recent work shows that several identified K(+) channels are important in both physiological and pathological cell proliferation and open a promising pathway for novel targeted therapies.

We have cloned a mammalian (rat) homologue of Drosophila ether á go‐go (eag) cDNA, which encodes a distinct type of voltage activated potassium (K) channel. The derived Drosophila and rat eag polypeptides share > 670 amino acids, with a sequence identity of 61%, exhibiting a high degree of similarity at the N‐terminus, the hydrophobic core including the pore forming P region and a potential cyclic nucleotide binding site. Rat eag mRNA is specifically expressed in the central nervous system. In the Xenopus oocyte expression system rat eag mRNA gives rise to voltage activated K channels which have distinct properties in comparison with Drosophila eag channels and other voltage activated K channels. Thus, the rat eag channel further extends the known diversity of K channels. Most notably, the kinetics of rat eag channel activation depend strongly on holding membrane potential. Hyperpolarization slows down the kinetics of activation; conversely depolarization accelerates the kinetics of activation. This novel K channel property may have important implications in neural signal transduction allowing neurons to tune their repolarizing properties in response to membrane hyperpolarization.

Extracellular potassium concentration is actively tained within narrow limits in all higher oranisms.Slight variations in extraceliular potassium levels can induce major alterations of essential physiological functions in excitable tissues. Here we describe that superfusion of cultured rat hippocampal neurones with potassium-free medium leads to a decrease of a specific outward potassium current, probably carried by RCK4-type channels (RCK4 are potassium chans found in rat brain). This is confirmed by heterologous expression of these channels in Xenopus oocytes. (7).Electrophysiological Measurements. Whole-cell currents in cultured hippocampal neurones were measured by using Kimax glass pipettes having resistances of 4-5 MU and filled with a solution ofthe following composition: 100 mM KCl, 10 mM NaCl, 20 mM phosphocreatine, 5 units of creatine phosphokinase per ml, 4 mM MgATP, 10 mM EGTA, and 10 mM Hepes-KOH (pH 7.2). The bath solution contained 140 mM NaCl, 2 mM CaCl2, 2 mM MgCl2, 200 nM tetrodotoxin, 5 mM tetraethylammonium, 10 nM charybdotoxin, and 10 mM Hepes-NaOH (pH 7.2), with or without 2.8 mM KCl.For heterologous expression of RCK4 channels (K+ channels found in rat brain cortex), the specific cDNA-derived mRNA (cRNA) was injected into oocytes (average amount 25 pg per oocyte) and the currents were recorded 2-5 days after injection. The electrophysiological recordings on whole oocytes were performed under conventional voltage-clamp conditions by using a Turbo-TEC amplifier (NPI Electronics, Tamm, F.R.G.) and intracellular electrodes with resistances of 0.6-0.8 MU when filled with 2 M KCl. All pulse protocols were designed with 20-s intervals between pulses to allow complete recovery from inactivation of the channel. Leak and capacitive currents were subtracted on-line by using a P/6 method. During the recording, the oocyte was continuously superfused with the test solution at a flow rate of 10 ml/min; the chamber volume was about 0.3 ml.The current induced by depolarizing steps was also measured in outside-out membrane patches under constant flow of a bathing solution containing various concentrations of cations. For this purpose, we used aluminium-silicate pipettes with resistances of 0.8-1.2 MU, filled with 100 mM KCI/10 mM EGTA/10 mM Hepes-KOH, pH 7.2. The bath solution contained 120 mM Tris, 1.8 mM CaC12, and 10 mM Hepes (pH 7.2 adjusted with HCl). The cations tested were added to this solution as chloride salts, always maintaining the total concentration of monovalent cations to 120 mM.The gating charge measurement was performed in outsideout patches as described (8), with 120 mM Tris chloride, pH 7.2/10 mM EGTA as pipette solution.All electrophysiological experiments were performed at 19-210C. Pulse patterns were generated, and currents were sampled with a VME-bus-based computer system. RESULTS Reduction 2466The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 so...

The Drosophila ether-à-go-go (eag) mutant is responsible for altered potassium currents in excitable tissue. These mutants exhibit spontaneous, repetitive firing of action potentials in the motor axons of larval neuromuscular junctions. The eag gene encodes a polypeptide that shares sequence similarities with several different ionic channel proteins, including voltage-gated potassium channels, an inward rectifier as well as cyclic-nucleotide-gated channels. These formal similarities in the derived primary sequences indicate that eag polypeptides might express a new type of ion channel. Here we report the expression by eag RNA in Xenopus oocytes of such a channel which incorporates properties of both voltage- and ligand-gated channels. The permeability of these eag channels to potassium and calcium is dependent on voltage and cyclic AMP. The ability to mediate potassium-outward and calcium-inward currents endows this channel with properties likely to be important in the modulation of synaptic efficiency in both central and peripheral nervous systems.