New opportunities and challenges of venom-based and bacteria-derived molecules for anticancer targeted therapy

Due to advances in detection and treatment of cancer, especially the rise in the targeted therapy, the five-year relative survival rate of all cancers has increased significantly. However, according to the analysis of the survival rate of cancer patients in 2019, the survival rate of most cancers is still less than five years. Therefore, to combat complex cancer and further improve the 5-year survival rate of cancer patients, it is necessary to develop some new anticancer drugs. Because of the adaptive evolution of toxic species for millions of years, the venom sac is a "treasure bank", which has millions of biomolecules with high affinity and stability awaiting further development. Complete utilization of venom-based and bacteria-derived drugs in the market is still staggering because of incomplete understanding regarding their mode of action. In this review, we focused on the currently identified targets for anticancer effects based on venomous and bacterial biomolecules, such as ion channels, membrane non-receptor molecules, integrins, and other related target molecules. This review will serve as the key for exploring the molecular mechanisms behind the anticancer potential of venom-based and bacteria-derived drugs and will also lay the path for the development of anticancer targeted therapy.

Voltage-dependent K+ currents contribute to heterogeneity of olfactory ensheathing cells

The olfactory nerve is permissive for axon growth throughout life. This has been attributed in part to the olfactory ensheathing glial cells that encompass the olfactory sensory neuron fascicles. Olfactory ensheathing cells (OECs) also promote axon growth in vitro and when transplanted in vivo to sites of injury. The mechanisms involved remain largely unidentified owing in part to the limited knowledge of the physiological properties of ensheathing cells. Glial cells rely for many functions on the properties of the potassium channels expressed; however, those expressed in ensheathing cells are unknown. Here we show that OECs express voltage-dependent potassium currents compatible with inward rectifier (Kir ) and delayed rectifier (KDR ) channels. Together with gap junction coupling, these contribute to the heterogeneity of membrane properties observed in OECs. The relevance of K(+) currents expressed by ensheathing cells is discussed in relation to plasticity of the olfactory nerve.

L-Type Ca(2+) Channels and SK Channels in Mouse Embryonic Stem Cells and Their Contribution to Cell Proliferation

Mouse embryonic stem cells (mESCs) are capable of both self-renewal and multilineage differentiation; thus, they can be expanded in vivo or in vitro and differentiated to produce different cell types. Despite their biological and medical interest, many physiological properties of undifferentiated mESCs, such as ion channel function, are not fully understood. Ion channels are thought to be involved in cell proliferation and differentiation. The aim of this study was to characterize functional ion channels in cultured undifferentiated mESCs and their role in cell proliferation. L-type voltage-activated Ca(2+) channels sensitive to nifedipine and small-conductance Ca(2+)-activated K(+) (SK) channels sensitive to apamin were identified. Ca(2+)-activated K(+) currents were blocked by millimolar concentrations of tetraethylammonium. The effects of Ca(2+) channel and Ca(2+)-activated K(+) channel blockers on the proliferation of undifferentiated mESCs were investigated by bromodeoxyuridine (BrdU) incorporation. Dihydropyridine derivatives, such as nifedipine, inhibited cell growth and BrdU incorporation into the cells, whereas apamin, which selectively blocks SK channels, had no effect on cell growth. These results demonstrate that functional voltage-operated Ca(2+) channels and Ca(2+)-activated K(+) channels are present in undifferentiated mESCs. Moreover, voltage-gated L-type Ca(2+) channels, but not SK channels, might be necessary for proliferation of undifferentiated mESCs.

Brain natriuretic peptide modulates the delayed rectifier outward K(+) current and promotes the proliferation of mouse Schwann cells

Brain natriuretic peptide (BNP) may act as a neuromodulator via its associated receptors (natriuretic peptide receptors, NPRs) in the central nervous system (CNS), but few studies have reported its activity in the peripheral nervous system (PNS). In this study, we observed that BNP increased the tetraethylammonium chloride (TEA)-sensitive delayed rectifier outward potassium current (I(K)) in mouse Schwann cells (SCs) using whole-cell recording techniques. At concentrations of 1-100 nM, BNP reversibly activated I(K) in a dose-dependent manner, with modulating its steady-state activation and inactivation properties. The effect of BNP on I(K) was abolished by preincubation with the specific antagonist of NPR-A, and could not be mimicked by application of NPR-C agonist. These results were supported by immunocytochemical findings indicating that NPR-A was expressed in SCs. The application of 8-Br-guanosine 3',5'-monophosphate (8-Br-cGMP) mimicked the effect of BNP on I(K), but BNP was unable to further increase I(K) after the application of cyclic guanosine monophosphate (cGMP). Genistein blocked I(K) and also completely eliminated the effects of BNP and cGMP on I(K). The selective K(V)2.1 subunit blocker, Jingzhaotoxin-III (JZTX-III), reduced I(K) amplitude by 30%, but did not abolish the increase effect of BNP on I(K) amplitude. In addition, BNP significantly stimulated SCs proliferation and this effect could be partly inhibited by TEA. Together these results suggest that BNP modulated I(K) probably via cGMP- and tyrosine kinase-dependent pathways by activation of NPR-A. This effect of BNP on I(K) in SCs might partly explain its effect on cell proliferation.

Chloride channel blockers inhibit iNOS expression and NO production in IFNgamma-stimulated microglial BV2 cells

Microglial cells play an important role during neuroinflammation in the central nervous system. Among other factors, activated microglia produce nitric oxide (NO), which is toxic to neurons and excessive microglial activation and NO production contribute to the pathology of neurodegenerative diseases. Chloride channels have previously been shown to participate in microglial activation. Here we investigate the effects of established chloride channel blockers with different chemical structures on interferon-gamma (IFNgamma)-induced activation of the murine microglial cell line, BV2. IFNgamma-induced NO production was effectively reduced by NPPB, IAA-94, tamoxifen, NS3728 and NS1652, with NS1652 being the most potent. In contrast, DIDS reduced NO production only at cytotoxic concentrations. Furthermore, NS1652 reduced the protein and mRNA levels of inducible nitric oxide synthase (iNOS), without altering STAT1 phosphorylation. These observations suggest a microglial chloride conductance as a critical permissive factor downstream in the IFNgamma-induced iNOS cascade. The nature of the underlying channel is unknown, but the pharmacological profile appears incompatible with the involvement of the volume activated anion conductance (VRAC).

Bradykinin inhibits the transient outward K+ current in mouse Schwann cells via the cAMP/PKA pathway

Bradykinin (BK) is an endogenous peptide with diverse biological actions and is considered to be an important mediator of the inflammatory response in both the peripheral and the central nervous systems. BK has attracted recent interest as a potential mediator of K(+) conductance, Cl(-) channels, and Ca(2+)-activated K(+) channels. However, few reports have associated BK with the voltage-gated K(+) current. In this study, we demonstrated that BK suppressed the transient outward potassium current (I(A)) in mouse Schwann cells using whole cell recording techniques. At a concentration of 0.1 muM to 5 muM, BK reversibly inhibited I(A) in a dose-dependent manner with the modulation of steady-state activation and inactivation properties. The effect of BK on I(A) current was abolished after preincubation with a B(2) receptor antagonist but could not be eliminated by B(1) receptor antagonist. Intracellular application of GTP-gammaS induced an irreversible decrease in I(A), and the inhibition of G(s) using NF449 provoked a gradual augmentation in I(A) and eliminated the BK-induced effect on I(A,) while the G(i)/(o) antagonist NF023 did not. The application of forskolin or dibutyryl-cAMP mimicked the inhibitory effect of BK on I(A) and abolished the BK-induced effect on I(A). H-89, an inhibitor of PKA, augmented I(A) amplitude and completely eliminated the BK-induced inhibitory effect on I(A). In contrast, activation of PKC by PMA augmented I(A) amplitude. A cAMP assay revealed that BK significantly increased intracellular cAMP level. It is therefore concluded that BK inhibits the I(A) current in Schwann cells by cAMP/PKA-dependent pathways via activation of the B(2) receptor.

Physiology of cell volume regulation in vertebrates

The ability to control cell volume is pivotal for cell function. Cell volume perturbation elicits a wide array of signaling events, leading to protective (e.g., cytoskeletal rearrangement) and adaptive (e.g., altered expression of osmolyte transporters and heat shock proteins) measures and, in most cases, activation of volume regulatory osmolyte transport. After acute swelling, cell volume is regulated by the process of regulatory volume decrease (RVD), which involves the activation of KCl cotransport and of channels mediating K(+), Cl(-), and taurine efflux. Conversely, after acute shrinkage, cell volume is regulated by the process of regulatory volume increase (RVI), which is mediated primarily by Na(+)/H(+) exchange, Na(+)-K(+)-2Cl(-) cotransport, and Na(+) channels. Here, we review in detail the current knowledge regarding the molecular identity of these transport pathways and their regulation by, e.g., membrane deformation, ionic strength, Ca(2+), protein kinases and phosphatases, cytoskeletal elements, GTP binding proteins, lipid mediators, and reactive oxygen species, upon changes in cell volume. We also discuss the nature of the upstream elements in volume sensing in vertebrate organisms. Importantly, cell volume impacts on a wide array of physiological processes, including transepithelial transport; cell migration, proliferation, and death; and changes in cell volume function as specific signals regulating these processes. A discussion of this issue concludes the review.

Cell volume regulation: physiology and pathophysiology

Cell volume perturbation initiates a wide array of intracellular signalling cascades, leading to protective and adaptive events and, in most cases, activation of volume-regulatory osmolyte transport, water loss, and hence restoration of cell volume and cellular function. Cell volume is challenged not only under physiological conditions, e.g. following accumulation of nutrients, during epithelial absorption/secretion processes, following hormonal/autocrine stimulation, and during induction of apoptosis, but also under pathophysiological conditions, e.g. hypoxia, ischaemia and hyponatremia/hypernatremia. On the other hand, it has recently become clear that an increase or reduction in cell volume can also serve as a specific signal in the regulation of physiological processes such as transepithelial transport, cell migration, proliferation and death. Although the mechanisms by which cell volume perturbations are sensed are still far from clear, significant progress has been made with respect to the nature of the sensors, transducers and effectors that convert a change in cell volume into a physiological response. In the present review, we summarize recent major developments in the field, and emphasize the relationship between cell volume regulation and organism physiology/pathophysiology.

Cell volume regulatory ion channels in cell proliferation and cell death

Alterations of cell volume are key events during both cell proliferation and apoptotic cell death. Cell proliferation eventually requires an increase of cell volume, and apoptosis is typically paralleled by cell shrinkage. Alterations of cell volume require the participation of ion transport across the cell membrane, including appropriate activity of Cl(-) and K(+) channels. Cl(-) channels modify cytosolic Cl(-) activity and mediate osmolyte flux, and thus influence cell volume. Most Cl(-) channels allow exit of HCO(3)(-), leading to cytosolic acidification, which in turn inhibits cell proliferation and favors apoptosis. K(+) exit through K(+) channels decreases cytosolic K(+) concentration, which may sensitize the cell for apoptotic cell death. K(+) channel activity further maintains the cell membrane potential, a critical determinant of Ca(2+) entry through Ca(2+) channels. Ca(2+) may, in addition, enter through Ca(2+)-permeable cation channels, which, in some cells, are activated by hyperosmotic shock. Increases of cytosolic Ca(2+) activity may trigger both mechanisms required for cell proliferation and mechanisms, leading to apoptosis. Thereby cell proliferation and apoptosis depend on magnitude and temporal organization of Ca(2+) entry, as well as activity of other signaling pathways. Accordingly, the same ion channels may participate in the stimulation of both cell proliferation and apoptosis. Specific ion channel blockers may thus abrogate both cellular mechanisms, depending on cell type and condition.

Ion channels in mesenchymal stem cells from rat bone marrow

Mesenchymal stem cells (MSCs) from bone marrow are believed to be an ideal cell source for cardiomyoplasty; however, cellular electrophysiology is not understood. The present study was designed to investigate ion channels in undifferentiated rat MSCs. It was found that three types of outward currents were present in rat MSCs, including a small portion of Ca(2+)-activated K(+) channel (I(KCa)) sensitive to inhibition by iberiotoxin and/or clotromazole, a delayed rectifier K(+) current (IK(DR)), and a transient outward K(+) current (I(to)). In addition, tetrodotoxin (TTX)-sensitive sodium current (I(Na.TTX)) and nifedipine-sensitive L-type Ca(2+) current (I(Ca.L)) were found in a small population of rat MSCs. Moreover, reverse transcription-polymerase chain reaction revealed the molecular evidence of mRNA for the functional ionic currents, including Slo and KCNN4 for I(KCa); Kv1.4 for I(to); Kv1.2 and Kv2.1 for IK(DR); SCN2a1 for I(Na.TTX); and CCHL2a for I(Ca.L). These results demonstrate for the first time that multiple functional ion channel currents (i.e., I(KCa), I(to), IK(DR), I(Na.TTX), and I(Ca.L)) are present in rat MSCs from bone marrow; however, physiological roles of these ion channels remain to be studied.

Role of voltage-gated potassium channels in cancer

Ion channels are being associated with a growing number of diseases including cancer. This overview summarizes data on voltage-gated potassium channels (VGKCs) that exhibit oncogenic properties: ether-à-go-go type 1 (Eag1). Normally, Eag1 is expressed almost exclusively in tissue of neural origin, but its ectopic expression leads to uncontrolled proliferation, while inhibition of Eag1 expression produces a concomitant reduction in proliferation. Specific monoclonal antibodies against Eag1 recognize an epitope in over 80% of human tumors of diverse origins, endowing it with diagnostic and therapeutic potential. Eag1 also possesses unique electrophysiological properties that simplify its identification. This is particularly important, as specific blockers of Eag1 currents are not available. Molecular imaging of Eag1 in live tumor models has been accomplished with dye-tagged antibodies using 3-D imaging techniques in the near-infrared spectral range.

Ion channels in cell proliferation and apoptotic cell death

Cell proliferation and apoptosis are paralleled by altered regulation of ion channels that play an active part in the signaling of those fundamental cellular mechanisms. Cell proliferation must--at some time point--increase cell volume and apoptosis is typically paralleled by cell shrinkage. Cell volume changes require the participation of ion transport across the cell membrane, including appropriate activity of Cl- and K+ channels. Besides regulating cytosolic Cl- activity, osmolyte flux and, thus, cell volume, most Cl- channels allow HCO3- exit and cytosolic acidification, which inhibits cell proliferation and favors apoptosis. K+ exit through K+ channels may decrease intracellular K+ concentration, which in turn favors apoptotic cell death. K+ channel activity further maintains the cell membrane potential, a critical determinant of Ca2+ entry through Ca2+ channels. Cytosolic Ca2+ may trigger mechanisms required for cell proliferation and stimulate enzymes executing apoptosis. The switch between cell proliferation and apoptosis apparently depends on the magnitude and temporal organization of Ca2+ entry and on the functional state of the cell. Due to complex interaction with other signaling pathways, a given ion channel may play a dual role in both cell proliferation and apoptosis. Thus, specific ion channel blockers may abrogate both fundamental cellular mechanisms, depending on cell type, regulatory environment and condition of the cell. Clearly, considerable further experimental effort is required to fully understand the complex interplay between ion channels, cell proliferation and apoptosis.

ATP binding cassette transporter ABC1 is required for the release of interleukin-1beta by P2X7-stimulated and lipopolysaccharide-primed mouse Schwann cells

Schwann cells are best known as myelinating glial cells of the peripheral nervous system, but they also participate actively in the sphere of immunity by producing pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta). In a previous study, we demonstrated that posttranslational processing of IL-1beta by immune-challenged Schwann cells required the P2X7 receptor. Remarkably, the release of IL-1beta was not associated with cell death, indicating the involvement of an active mechanism. ATP binding cassette (ABC) transporters are known to transport leaderless secretory proteins, such as IL-1beta; therefore, we investigated whether such transporters were at work in Schwann cells. Mouse Schwann cells expressed ABC1 transporter mRNA and displayed the functional protein. Glybenclamide and diisothiocyanato-stilbene-disulfonic acid (DIDS), two blockers of chloride fluxes that drive the export activity of ABC1 transporters, inhibited IL-1beta release without altering its intracellular processing. Enhancing chloride efflux potentiated the release of IL-1beta, while decreasing it led to a strong reduction in its release. Because the stimulation of the P2X7 receptor also activates a chloride conductance, we investigated the possibility of a sole anionic pathway mobilized by the P2X7 receptor and ABC1. Glybenclamide and DIDS had no significant effects on the P2X7-activated chloride current suggesting therefore the existence of two different pathways. In summary, ABC1 transporters are required for the release of IL-1beta by mouse Schwann cells. Being associated together with chloride conductance, P2X7 receptors and ABC1 transporters delineate a subtle and complex regulation of IL-1beta production in mammalian Schwann cells. Furthermore, ABC1 transporters could be a target of therapeutic interest for regulating IL-1beta activity in neuroinflammation disorders.

Blockage of intermediate-conductance Ca2+-activated K+ channels inhibit human pancreatic cancer cell growth in vitro

Ion channels are important in controlling cell cycle progression and proliferation in a variety of cell types. Using the whole-cell recording mode of the patch-clamp technique, functional ion channels were electrophysiologically characterized in PANC-1 (K-ras G12D (+/-), p53 R273C, Deltap16), BxPC-3 (smad4-, p53 Y220C, Deltap16), and MiaPaCa-2 [transforming growth factor-beta receptor type II defect, K-ras G12C(-/-), p53 R248W, Deltap16] human pancreatic cancer cell lines. In BxPC-3 and the MiaPaCa-2 cells, we could identify approximately 600 or approximately 1200 functional Ca2+-activated K+ channels (IK) per cell, respectively, whereas PANC-1 cells expressed approximately 200 functional IK channels per cell. These channels were observed by using pipette solutions buffering [Ca2+]i to 1 microM. The channels were voltage-independent, blocked by charybdotoxin, clotrimazole, 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34), and blocked by Ba2+ in a voltage-dependent manner. In the presence of 10 microM clotrimazole or TRAM-34, proliferation of the BxPC-3 as well as the MiaPaCa-2 cells was completely stopped. In contrast, proliferation of PANC-1 cells was hardly affected by clotrimazole or TRAM-34. Proliferation in all three cell lines could be inhibited in the presence of the Ca2+ channel antagonists verapamil, diltiazem, and nifedipine. By quantitative RT-PCR, we could show that MiaPaCa-2 cells exhibit a 2.8-fold and BxPC3 cells a more than 8-fold elevated level of IK mRNA level compared with PANC-1 cells. Interestingly, in primary pancreatic tumors we found a tremendous up-regulation of IK mRNA. In eight of nine (or 89%) primary pancreatic tumor tissues, we found a 6- to 66-fold increase in IK mRNA. Our findings suggest that a certain amount of functional IK channels is crucial for the proliferation of some pancreatic cancer types. The blockade of IK channels may ultimately prove useful as a therapeutic option for some patients with ductal adenocarcinoma of the pancreas with an up-regulated IK channel expression.

Voltage-Gated ion currents of schwann cells in cell culture models of human neurofibromatosis

K(+) (K) channels play a role in the proliferation of many cell types in normal cells and certain disease states. Several laboratories have studied K currents in cultured Schwann cells from models of the human diseases, neurofibromatosis type 1 (NF1) and neurofibromatosis type 2 (NF2). These diseases are characterized by the growth of Schwann cell tumors. In all cell culture NF models the K current properties differ in tumor-derived and normal Schwann cells. Depending on the model however, the type of K channel abnormality differs. K channels appear to play a role in the proliferation of Schwann cell cultures of these disease models, because a link has been established between K current blockade and the inhibition of Schwann cell proliferation in NF1 and NF2. Differences in the proliferation response of normal Schwann cells to K channel blockers suggest that in vitro regulation of proliferation in neoplastic and normal Schwann cells is complex.

Biophysical properties and ionic signature of neuronal progenitors of the postnatal subventricular zone in situ

Previous studies have reported the presence of neuronal progenitors in the subventricular zone (SVZ) and rostral migratory stream (RMS) of the postnatal mammalian brain. Although many studies have examined the survival and migration of progenitors after transplantation and the factors influencing their proliferation or differentiation, no information is available on the electrophysiological properties of these progenitors in a near-intact environment. Thus we performed whole cell and cell-attached patch-clamp recordings of progenitors in brain slices containing either the SVZ or the RMS from postnatal day 15 to day 25 mice. Both regions displayed strong immunoreactivity for nestin and neuron-specific class III beta-tubulin, and recorded cells displayed a morphology typical of the neuronal progenitors known to migrate throughout the SVZ and RMS to the olfactory bulb. Recorded progenitors had depolarized zero-current resting potentials (mean more depolarized than -28 mV), very high input resistances (about 4 GOmega), and lacked action potentials. Using the reversal potential of K+ currents through a cell-attached patch a mean resting potential of -59 mV was estimated. Recorded progenitors displayed Ca2+-dependent K+ currents and TEA-sensitive-delayed rectifying K+ (KDR) currents, but lacked inward K+ currents and transient outward K+ currents. KDR currents displayed classical kinetics and were also sensitive to 4-aminopyridine and alpha-dendrotoxin, a blocker of Kv1 channels. Na+ currents were found in about 60% of the SVZ neuronal progenitors. No developmental changes were observed in the passive membrane properties and current profile of neuronal progenitors. Together these data suggest that SVZ neuronal progenitors display passive membrane properties and an ionic signature distinct from that of cultured SVZ neuronal progenitors and mature neurons.

Delayed rectifier K currents in NF1 Schwann cells. Pharmacological block inhibits proliferation

K+(K) currents are related to the proliferation of many cell types and have a relationship to second messenger pathways implicated in regulation of the cell cycle in development and certain disease states. We examined the role of K currents in Schwann cells (SC) cultured from tumors that arise in the human disease neurofibromatosis type 1 (NF1). Comparisons were made between whole cell voltage clamp recordings from normal human SC cultures and from neurofibroma cultures and malignant peripheral nerve sheath tumor (MPNST) cell lines. The outward K currents of normal and tumor cells could be divided into three types based on pharmacology and macroscopic inactivation: (1) "A type" current blocked by 4-aminopyridine, (2) delayed rectifier (DR) current blocked by tetraethylammonium, and (3) biphasic current consisting of a combination of these two current types. The DR K current was present in MPNST- and neurofibroma-derived SC, but not in quiescent, nondividing, normal SC. DR currents were largest in MPNST-derived SC (50 pA/pF vs. 2.1-4.9 pA/pF in dividing and quiescent normal SC). Normal SC cultures had significantly more cells with A type current than cultures of MPNST and the plexiform neurofibroma. Conversely, MPNST and plexiform neurofibroma cultures had significantly more SC with DR current than did normal cultures, and these DR currents were significantly larger. In addition, the plexiform neurofibroma culture had significantly more cells with DR current than the dermal neurofibroma culture. K currents in SC from normal NF1 SC cultures had current abundances similar to GGF-exposed normal SC and the plexiform neurofibroma. We have established a link between DR K current blockade via TEA analogs and inhibition of proliferation of NF1 SC in vitro. In addition, a farnysyl transferase inhibitor (FTI), a blocker of Ras activation, blocked cell proliferation without blocking K currents in all cultures except a plexiform neurofibroma, suggesting that regulation of proliferation in neoplastic and normal SC in vitro is complex.

PDGF upregulates delayed rectifier via Src family kinases and sphingosine kinase in oligodendroglial progenitors

An increase in the expression of the delayed rectifier current (I(K)) has been shown to correlate with mitogenesis in many cell types. However, pathways involved in the upregulation of I(K) by growth factors in oligodendroglial progenitors (OPs) have not been well-elucidated. In this study, we found that treatment with platelet-derived growth factor (PDGF) and basic fibroblast growth factor but not ciliary neurotrophic factor resulted in increased I(K) density and upregulation of Kv1.5 and Kv1.6 mRNA transcripts. The effect of PDGF on I(K) was blocked by mimosine, a cell cycle inhibitor, and by genistein, a tyrosine kinase inhibitor. Using inhibitors of PDGF-activated pathways, we found that PDGF-induced upregulation of Kv1.5 and I(K) density involves Src family tyrosine kinases, sphingosine kinase, and intracellular Ca(2+) but not ERK1/2 or phosphatidylinositol 3-kinase pathways. Furthermore, agents that were effective inhibitors of PDGF-induced I(K) upregulation also attenuated OP proliferation, supporting the concept that I(K) is an important link between PDGF-activated signaling cascades and cell cycle progression.

Cell cycle-dependent expression of volume-activated chloride currents in nasopharyngeal carcinoma cells

Patch-clamping and cell image analysis techniques were used to study the expression of the volume-activated Cl(-) current, I(Cl(vol)), and regulatory volume decrease (RVD) capacity in the cell cycle in nasopharyngeal carcinoma cells (CNE-2Z). Hypotonic challenge caused CNE-2Z cells to swell and activated a Cl(-) current with a linear conductance, negligible time-dependent inactivation, and a reversal potential close to the Cl(-) equilibrium potential. The sequence of anion permeability was I(-) > Br(-) > Cl(-) > gluconate. The Cl(-) channel blockers tamoxifen, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), and ATP inhibited I(Cl(vol)). Synchronous cultures of cells were obtained by the mitotic shake-off technique and by a double chemical-block (thymidine and hydroxyurea) technique. The expression of I(Cl(vol)) was cell cycle dependent, being high in G(1) phase, downregulated in S phase, but increasing again in M phase. Hypotonic solution activated RVD, which was cell cycle dependent and inhibited by the Cl(-) channel blockers NPPB, tamoxifen, and ATP. The expression of I(Cl(vol)) was closely correlated with the RVD capacity in the cell cycle, suggesting a functional relationship. Inhibition of I(Cl(vol)) by NPPB (100 microM) arrested cells in G(0)/G(1). The data also suggest that expression of I(Cl(vol)) and RVD capacity are actively modulated during the cell cycle. The volume-activated Cl(-) current associated with RVD may therefore play an important role during the cell cycle progress.

Regulatory volume decrease is actively modulated during the cell cycle

Nasopharyngeal carcinoma cells, CNE-2Z, when swollen by 47% hypotonic solution, exhibited a regulatory volume decrease (RVD). The RVD was inhibited by extracellular applications of the chloride channel blockers tamoxifen (30 microM; 61% inhibition), 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 100 microM; 60% inhibition), and ATP (10 mM; 91% inhibition). The level and time constant of RVD varied greatly between cells. Most cells conducted an incomplete RVD, but a few had the ability to recover their volume completely. There was no obvious correlation between cell volume and RVD capacity. Flow cytometric analysis showed that highly synchronous cells were obtained by the mitotic shake-off technique and that the cells progressed through the cell cycle synchronously when incubated in culture medium. Combined application of DNA synthesis inhibitors, thymidine and hydroxyurea arrested cells at the G1/S boundary and 87% of the cells reached S phase 4 h after being released. RVD capacity changed significantly during the cell cycle progression in cells synchronized by shake-off technique. RVD capacity being at its highest in G1 phase and lowest in S phase. The RVD capacity in G1 (shake-off cells sampled after 4 h of incubation), S (obtained by chemical arrest), and M cells (selected under microscope) was 73, 33, and 58%, respectively, and the time constants were 435, 769, and 2,000 sec, respectively. We conclude that RVD capacity is actively modulated in the cell cycle and RVD may play an important role in cell cycle progress.

Chloride/anion channels in glial cell membranes

At least seven different chloride/anion currents have now been identified in astrocytes, oligodendrocytes/Schwann cells, and microglia. Only for two of these currents is the corresponding gene known. One of these genes is not encoding for a chloride channel, but for a class of mitochondria-like pores also found in cell membranes. Astrocytes and oligodendrocytes differ in their resting properties: astrocytes accumulate chloride but do not have a significant permeability. Oligodendrocytes have a close to passive distribution and a significant permeability. Under certain circumstances, astrocytes can express a resting chloride conductance. Reactive and neoplastic astrocytes as well as astrocytes with an altered shape exhibit a resting conductance. The function of these channels certainly involves volume regulation. Other possible functions are potassium homeostasis, migration, proliferation (in microglia), and involvement in spreading depression waves. Of greatest interest are two phenomena discovered in situ: The ClC-2 channel is only found in astrocytic endfeet near blood capillaries adjacent to neuronal GABA(A) receptors. In the supraoptic nucleus of the hypothalamus, there is an osmosensitive astrocytic taurine release. This released taurine interacts with glycine receptors in neighboring neurons, causing inhibition. It is assumed that with the future availability of more in situ, rather than in vitro, studies, an increased number of such complex interactions between glial cells, neurons, and blood vessels will be discovered.

Effects of Cl- channel blockers on endothelin-1-induced proliferation of rat vascular smooth muscle cells

The effects of Cl- channel blockers on endothelin-1 (ET-1)-induced proliferation of rat aortic vascular smooth muscle cells (VSMC) were examined. We found ET-1 concentration-dependently increased cell count and [3H]-thymidine incorporation into VSMC, with EC50 values of 24.8 and 11.4 nM, respectively. Both nifedipine and SK&F96365 inhibited 10 nM ET-1-induced [3H]-thymidine incorporation into VSMC with the maximal inhibitory concentrations of 1 and 10 microM, respectively. DIDS inhibited 10 nM ET-1-induced increase in cell count and [3H]-thymidine incorporation into VSMC in a concentration-dependent manner, whereas other Cl- channel blockers including IAA-94, NPPB, DPC, SITS and furosemide did not produce these effects. 3 microM DIDS reduced 10 nM ET-1-induced sustained increase in cytoplasmic Ca2+ concentration ([Ca2+]) by 52%. Pretreatment of VSMC with 1 microM nifedipine completely inhibited the DIDS effect on 10 nM ET-1-induced [3H]-thymidine incorporation into VSMC and sustained increase in [Ca2+]i, whereas pretreatment with 10 microM SK&F96365 did not completely block these effects of DIDS. DIDS did not affect ET-1-induced Ca2+ release and 30 mM KCl-induced increase in [Ca2+]i. Our data suggest that DIDS-sensitive Cl- channels mediate VSMC proliferation induced by ET-1 by mechanisms related to membrane depolarization and Ca2+ influx through voltage-dependent Ca2+ channels.

Electrophysiology of mammalian Schwann cells

Schwann cells are the satellite cell of the peripheral nervous system, and they surround axons and motor nerve terminals. The review summarises evidence for the ion channels expressed by mammalian Schwann cells, their molecular nature and known or speculated functions. In addition, the recent evidence for gap junctions and cytoplasmic diffusion pathways within the myelin and the functional consequences of a lower-resistance myelin sheath are discussed. The main types of ion channel expressed by Schwann cells are K(+) channels, Cl(-) channels, Na(+) channels and Ca(2+) channels. Each is represented by a variety of sub-types. The molecular and biophysical characteristics of the cation channels expressed by Schwann cells are closely similar or identical to those of channels expressed in peripheral axons and elsewhere. In addition, Schwann cells express P(2)X ligand-gated ion channels. Possible in vivo roles for each ion channel type are discussed. Ion channel expression in culture could have a special function in driving or controlling cell proliferation and recent evidence indicates that some Ca(2+) channel and Kir channel expression in culture is dependent upon the presence of neurones and local electrical activity.

The nuclear chloride ion channel NCC27 is involved in regulation of the cell cycle

NCC27 is a nuclear chloride ion channel, identified in the PMA-activated U937 human monocyte cell line. NCC27 mRNA is expressed in virtually all cells and tissues and the gene encoding NCC27 is also highly conserved. Because of these factors, we have examined the hypothesis that NCC27 is involved in cell cycle regulation. Electrophysiological studies in Chinese hamster ovary (CHO-K1) cells indicated that NCC27 chloride conductance varied according to the stage of the cell cycle, being expressed only on the plasma membrane of cells in G2/M phase. We also demonstrate that Cl- ion channel blockers known to block NCC27 led to arrest of CHO-K1 cells in the G2/M stage of the cell cycle, the same stage at which this ion channel is selectively expressed on the plasma membrane. These data strongly support the hypothesis that NCC27 is involved, in some as yet undetermined manner, in regulation of the cell cycle.

Enhanced proliferation and potassium conductance of Schwann cells isolated from NF2 schwannomas can be reduced by quinidine

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease that is characterized mainly by schwannomas, as well as menigiomas and gliomas. The NF2 gene product merlin/schwannomin acts as a tumor suppressor. Schwann cells derived from NF2 schwannomas showed an enhanced proliferation rate, and electrophysological studies revealed larger K(+) outward currents as compared with controls. Schwann cells isolated from schwannomas of NF2 patients or multiorgan donors were treated with different concentrations of the K(+) current blockers quinidine, tetraethylammonium chloride, and 4-aminopyridine and K(+) outward currents and proliferation rates of these cells were compared. K(+) outward currents of both cell types can be blocked by quinidine. Importantly, treatment with quinidine reduces proliferation of NF2 Schwann cells in a concentration dependent manner but did not reduce proliferation of normal Schwann cells. Therefore, the use of quinidine or quinidine-like components would possibly provide a novel adjuvant therapeutic option for NF2 patients to slow down or freeze growth of schwannomas.

The development of excitatory capability in Aplysia californica bag cells observed in cohorts

The bag cells of Aplysia release egg laying hormone in sexually mature animals. Bag cells cannot sustain the long-lasting excitatory afterdischarge (AD) required for hormone release prior to sexual maturity (T.A. Nick, L.K. Kaczmarek, T.J. Carew, Ionic currents underlying developmental regulation of repetitive firing in Aplysia bag cell neurons, J. Neurosci. 1996;16:7583-7598; L.A. Fieber, Characterization of Na(+) and Ca(2+) currents in bag cells of sexually immature Aplysia californica, J. Exp. Biol. 1998;201:745-754). To investigate the development of bag cell excitability, whole-cell voltage-clamp experiments were executed in dissociated bag cells from four cohorts (batches) of hatchery-reared A. californica maintained at 13-15 degrees C. K(+) current densities, representing the sum of at least four different outward K(+) currents (Nick et al., 1996), declined significantly as a function of age, beginning at least 2-3 months before sexual maturity. The K(+) current decreases coincided with the first appearance of Na(+) and Ca(2+) currents in bag cells, which occurred at ages 6-7 months. Whole cell K(+) currents were not decreased significantly by a cAMP analog earlier than 1 month prior to the onset of reproductive activity. The frequency of observing Na(+) currents in whole cell recordings was low for developmental times earlier than sexual maturity. In one winter batch, both control and PMA-treated Na(+) currents increased significantly with age, and PMA-treated current densities were significantly greater than controls, but the other two batches studied had significant differences in Na(+) current frequency only at sexual maturity. Ca(2+) currents were reliably measured in more cells than were Na(+) currents. The Ca(2+) current frequency increased significantly with maturity in one winter batch. Ca(2+) currents were significantly increased by phorbol ester treatment beginning 6-8 weeks before reproductive activity in the two winter batches. These observations support the hypothesis that bag cell excitability is not fully developed until shortly before sexual maturity.

Effects of voltage-gated ion channel modulators on rat prostatic cancer cell proliferation: comparison of strongly and weakly metastatic cell lines

BACKGROUND

The strongly metastatic MAT-LyLu and the weakly metastatic AT-2 rat prostatic cancer cell lines have been shown to express voltage-gated ion channels differentially. In the present study, the possible contribution of voltage-gated ion channel activity to the proliferation of these cell lines was investigated, in a comparative approach.

METHODS

Several voltage-gated ion channel modulators were tested for their effects on proliferation over 54 hr, using an in vitro assay. The modes of action of the chemicals were monitored by electrophysiological (patch-clamp) recording.

RESULTS

The voltage-gated K(+) channel blockers 4-aminopyridine (4-AP; 2 mM), margatoxin (5 nM), charybdotoxin (4.5 nM), and verapamil (50 microM) inhibited the K(+) channels of both cell lines by between 38-65% and reduced the proliferation of the AT-2 cell line, in a dose-dependent manner, by 8-51%. However, only 4-AP reduced proliferation of the MAT-LyLu cell line. Tetrodotoxin (6 microM) blocked completely the voltage-gated Na(+) channel expressed selectively in the MAT-LyLu cell line, but had no effect on the proliferation of either cell line. On the other hand, the presumed Na(+) channel "opener" veratridine (10-50 microM) reduced significantly, in a dose-dependent manner, the proliferation of both cell lines by up to approximately 30%.

CONCLUSIONS

We conclude that the mechanism(s) controlling the proliferation of the weakly metastatic AT-2 cells involves voltage-gated K(+) channels. In contrast, the proliferation of strongly metastatic MAT-LyLu cells is much less dependent upon voltage-gated K(+) channel activity.

Ion channels in glial cells

Functional and molecular analysis of glial voltage- and ligand-gated ion channels underwent tremendous boost over the last 15 years. The traditional image of the glial cell as a passive, structural element of the nervous system was transformed into the concept of a plastic cell, capable of expressing a large variety of ion channels and neurotransmitter receptors. These molecules might enable glial cells to sense neuronal activity and to integrate it within glial networks, e.g., by means of spreading calcium waves. In this review we shall give a comprehensive summary of the main functional properties of ion channels and ionotropic receptors expressed by macroglial cells, i.e., by astrocytes, oligodendrocytes and Schwann cells. In particular we will discuss in detail glial sodium, potassium and anion channels, as well as glutamate, GABA and ATP activated ionotropic receptors. A majority of available data was obtained from primary cell culture, these results have been compared with corresponding studies that used acute tissue slices or freshly isolated cells. In view of these data, an active glial participation in information processing seems increasingly likely and a physiological role for some of the glial channels and receptors is gradually emerging.

Changes in ion channel expression accompany cell cycle progression of spinal cord astrocytes

Arrest of spinal cord astrocytes at defined stages of the cell cycle clock causes significant changes in the expression of voltage-activated Na(+) and K(+) currents. Arrest of actively proliferating astrocytes in G1/G0 by all-trans-retinoic acid induces premature expression of inwardly rectifying K(+) currents (IK(IR)) typically expressed only in differentiated astrocytes. By contrast, arrest in S phase by ara-C or Aphidicolin leads to a greater than twofold increase in "delayed" outwardly rectifying currents (IK(D)) and a concomitant decrease in IK(IR). Pharmacological blockade of IK(D) by TEA and 4AP caused proliferating astrocytes to arrest in G0/G1, suggesting that activity of these channels is required for G1/S checkpoint progression. Conversely, in quiescent astrocytes, inhibition of IK(IR) by 30 microM BaCl(2) led to an increase in astrocyte proliferation and to an increase in the number of cells in S phase from 5% to 26%. These data suggest that a downregulation of K(IR) promotes cell cycle progression through the G1/S checkpoint. Blockade of IK(IR) in actively proliferating cells, however, leads to an accumulation in G2/M, suggesting that reappearance of this current may be critical for progression beyond DNA synthesis. Interestingly, Na(+) currents (INa(+)) are increased greater than fourfold in S phase-arrested cells, yet their pharmacological blockade by TTX has no effect on cell cycle progression. However, the resting membrane potential of S phase-arrested cells increases profoundly, and manipulation of membrane potential by the application of low concentrations of ouabain, or reduction of extracellular potassium, induces the accumulation of quiescent astrocytes in S phase of the cell cycle, suggesting that either depolarization or intracellular sodium, or both, play an important role in promoting astrocyte proliferation.

Developmental changes in the expression of Shaker- and Shab-related K(+) channels in neurons of the rat trigeminal ganglion

We have investigated properties of voltage-gated K(+) channels in neurons of the pre- and postnatal rat trigeminal ganglion (TG). To correlate functional data with information on gene expression of Shaker- and Shab-related channels in these pseudo-unipolar neurons, the patch-clamp technique was combined with the single-cell reverse transcription-polymerase chain reaction (RT-PCR). A majority (80%) of prenatal TG neurons possessed only sustained delayed rectifier currents with half-maximal current inactivation at -30 mV. In the postnatal cells, steady-state inactivation of sustained currents occurred at more negative voltages (half-maximal inactivation at -58 mV). About 65% of the postnatal cells displayed a transient outward component in addition to the sustained currents. With increasing age, the sensitivity of sustained currents to 4-aminopyridine (4-AP) decreased significantly. The Shaker channel toxins, alpha-dendrotoxin and agitoxin-2 (50 and 10 nM), were much less effective. Discrimination between both stages with tetraethylammonium chloride (5 mM) was not possible since the currents were reduced generally by about 50%. After recording, the cell content was harvested and single-cell RT-PCR was performed to compare K(+) current properties and mRNA expression within the same cell. Most cells simultaneously expressed several different Shaker- and Shab-like transcripts. At postnatal day 14, the frequency of cells carrying transcripts encoding Kv1.1 decreased. Detailed analysis revealed a higher 4-AP sensitivity of TG neurons expressing Kv1.1 transcripts.

Differential inhibition of glial K(+) currents by 4-AP

Spinal cord astrocytes express four biophysically and pharmacologically distinct voltage-activated potassium (K(+)) channel types. The K(+) channel blocker 4-aminopyridine (4-AP) exhibited differential and concentration-dependent block of all of these currents. Specifically, 100 microM 4-AP selectively inhibited a slowly inactivating outward current (K(SI)) that was insensitive to dendrototoxin (< or = 10 microM) and that activated at -50 mV. At 2 mM, 4-AP inhibited fast-inactivating, low-threshold (-70 mV) A-type currents (K(A)) and sustained, TEA-sensitive noninactivating delayed-rectifier-type currents (K(DR)). At an even higher concentration (8 mM), 4-AP additionally blocked inwardly rectifying, Cs(+)- and Ba(2+)-sensitive K(+) currents (K(IR)). Current injection into current-clamped astrocytes in culture or in acute spinal cord slices induced an overshooting voltage response reminiscent of slow neuronal action potentials. Increasing concentrations of 4-AP selectively modulated different phases in the repolarization of these glial spikes, suggesting that all four K(+) currents serve different roles in stabilization and repolarization of the astrocytic membrane potential. Our data suggest that 4-AP is an useful, dose-dependent inhibitor of all four astrocytic K(+) channels. We show that the slowly inactivating astrocytic K(+) currents, which had not been described as separate current entities in astrocytes, contribute to the resting K(+) conductance and may thus be involved in K(+) homeostatic functions of astrocytes. The high sensitivity of these currents to micromolar 4-AP suggests that application of 4-AP to inhibit neuronal A-currents or to induce epileptiform discharges in brain slices also may influence astrocytic K(+) buffering.

PKC regulates turnover rate of rabbit intestinal Na+-glucose transporter expressed in COS-7 cells

We have used the recombinant NH2-terminal myc-tagged rabbit Na+-glucose transporter (SGLT1) to study the regulation of this carrier expressed in COS-7 cells. Treatment of cells with a protein kinase C (PKC) agonist, phorbol 12-myristate 13-acetate (PMA), caused a significant decrease (38.03 +/- 0.05%) in methyl alpha-D-glucopyranoside transport activity that could not be emulated by 4alpha-phorbol 12,13-didecanoate. The decrease in sugar uptake stimulated by PMA was reversed by the PKC inhibitor bisindolylmaleimide I. The maximal rate of Na+-glucose cotransport activity (Vmax) was decreased from 1.29 +/- 0.09 to 0.85 +/- 0.04 nmol. min-1. mg protein-1 after PMA exposure. However, measurement of high-affinity Na+-dependent phloridzin binding revealed that there was no difference in the number of cell surface transporters after PMA treatment; maximal binding capacities were 1.54 +/- 0.34 and 1.64 +/- 0.21 pmol/mg protein for untreated and treated cells, respectively. The apparent sugar binding affinity (Michaelis-Menten constant) and phloridzin binding affinity (dissociation constant) were not affected by PMA. Because PKC reduced Vmax without affecting the number of cell surface SGLT1 transporters, we conclude that PKC has a direct effect on the carrier, resulting in a lowering of the transporter turnover rate by a factor of two.