Single particle image reconstruction of the human recombinant Kv2.1 channel.

Kv2.1 channels are widely expressed in neuronal and endocrine cells and generate slowly activating K+ currents, which contribute to repolarization in these cells. Kv2.

Identification and characterisation of a new class of highly specific and potent inhibitors of the mitochondrial pyruvate carrier.

Two novel thiazolidine compounds, GW604714X and GW450863X, were found to be potent inhibitors of mitochondrial respiration supported by pyruvate but not other substrates. Direct measurement of pyruvate transport into rat liver and yeast mitochondria confirmed that these agents inhibited the mitochondrial pyruvate carrier (MPC) with K(i) values <0.1 muM.

Defective pancreatic beta-cell glycolytic signaling in hepatocyte nuclear factor-1alpha-deficient mice.

Mutations in the hepatocyte nuclear factor-1alpha (HNF-1alpha) gene cause maturity onset diabetes of the young type 3, a form of type 2 diabetes mellitus. In mice lacking the HNF-1alpha gene, insulin secretion and intracellular calcium ([Ca2+]i) responses were impaired following stimulation with nutrient secretagogues such as glucose and glyceraldehyde but normal with non-nutrient stimuli such as potassium chloride. Patch clamp recordings revealed ATP-sensitive K+ currents (KATP) in beta-cells that were insensitive to suppression by glucose but normally sensitive to ATP.

Characterization of a Ca2+ release-activated nonselective cation current regulating membrane potential and [Ca2+]i oscillations in transgenically derived beta-cells.

Although stimulation of insulin secretion by glucose is regulated by coupled oscillations of membrane potential and intracellular Ca2+ ([Ca2+]i), the membrane events regulating these oscillations are incompletely understood. In the presence of glucose and tetraethylammonium, transgenically derived beta-cells (betaTC3-neo) exhibit coupled voltage and [Ca2+]i oscillations strikingly similar to those observed in normal islets in response to glucose. Using these cells as a model system, we investigated the membrane conductance underlying these oscillations.

Genomic organization, chromosomal localization, tissue distribution, and biophysical characterization of a novel mammalian Shaker-related voltage-gated potassium channel, Kv1.7.

We report the isolation of a novel mouse voltage-gated Shaker-related K+ channel gene, Kv1.7 (Kcna7/KCNA7). Unlike other known Kv1 family genes that have intronless coding regions, the protein-coding region of Kv1.

Expression and function of pancreatic beta-cell delayed rectifier K+ channels. Role in stimulus-secretion coupling.

Voltage-dependent delayed rectifier K+ channels regulate aspects of both stimulus-secretion and excitation-contraction coupling, but assigning specific roles to these channels has proved problematic. Using transgenically derived insulinoma cells (betaTC3-neo) and beta-cells purified from rodent pancreatic islets of Langerhans, we studied the expression and role of delayed rectifiers in glucose-stimulated insulin secretion. Using reverse-transcription polymerase chain reaction methods to amplify all known candidate delayed rectifier transcripts, the expression of the K+ channel gene Kv2.

Chopart prosthesis and semirigid foot orthosis in traumatic forefoot amputation. Comparative gait analysis.

Gait was analyzed in seven otherwise healthy males at least 11 mo after they had recovered from a traumatic unilateral transmetatarsal amputation incurred during the course of their usual occupation. All seven were fitted with a semirigid foot orthosis. Four were also fitted with a Chopart prosthesis.

K+ channels: generating excitement in pancreatic beta-cells.

K+ channels play a key role in cellular physiology by regulating the efflux of K+ ions. They are the most diverse group of ion channel proteins; more than 30 K+ channel genes have been characterized. Regulated by ATP, voltage, and calcium, multiple K+ channels coexist in the beta-cell to regulate membrane potential, cell excitability, and insulin secretion.

Activation of stimulus-secretion coupling in pancreatic beta-cells by specific products of glucose metabolism. Evidence for privileged signaling by glycolysis.

The energy requirements of most cells supplied with glucose are fulfilled by glycolytic and oxidative metabolism, yielding ATP. In pancreatic beta-cells, a rise in cytosolic ATP is also a critical signaling event, coupling closure of ATP-sensitive K+ channels (KATP) to insulin secretion via depolarization-driven increases in intracellular Ca2+ ([Ca2+]i). We report that glycolytic but not Krebs cycle metabolism of glucose is critically involved in this signaling process.

NIDDM is associated with loss of pancreatic beta-cell L-type Ca2+ channel activity.

Development of non-insulin-dependent diabetes mellitus (NIDDM) is associated with defects in glucose-stimulated insulin secretion. We have investigated Zucker diabetic fatty rats (ZDF), an animal model of NIDDM, and found that, compared with control islets, the expression of mRNA encoding C- and D-isoforms of alpha 1-subunits of beta-cell L-type voltage-dependent Ca2+ channels (VDCC) was significantly reduced in islets isolated from ZDF rats. This correlated with a substantial reduction of L-type Ca2+ currents (ICa) in ZDF beta-cells.

Depletion of intracellular Ca2+ stores activates a maitotoxin-sensitive nonselective cationic current in beta-cells.

Glucose stimulation of beta-cell insulin secretion is initiated by membrane depolarization coupled with an elevation in intracellular Ca2+ concentration ([Ca2+]i). Both depolarization-dependent Ca2+ entry and intracellular Ca2+ store release contribute to the sugar-induced rise in [Ca2+]i. Here we show that maneuvers depleting intracellular Ca2+ stores induce membrane depolarization and a sustained nitrendipine-sensitive Ca2+ influx, whereas interventions promoting Ca2+ store refilling produce a hyperpolarization and inhibit Ca2+ influx.

Delayed rectifier K+ channel overexpression in transgenic islets and beta-cells associated with impaired glucose responsiveness.

Glucose stimulation of pancreatic beta-cell insulin secretion is closely coupled to alterations in ion channel conductances and intracellular Ca2+ ([Ca2+]i). To further examine this relationship after augmentation of voltage-dependent K+ channel expression, transgenic mice were produced which specifically overexpress a human insulinoma-derived, tetraethylammonium (TEA)-insensitive delayed rectifier K+ channel in their pancreatic beta-cells as shown by immunoblot of isolated islets and immunohistochemical analysis of pancreas sections. Whole-cell current recordings confirmed the presence of high amplitude TEA-resistant K+ currents in transgenic islet cells, whose expression correlated with hyperglycemia and hypoinsulinemia.

Defective glucose-dependent endoplasmic reticulum Ca2+ sequestration in diabetic mouse islets of Langerhans.

Non-insulin-dependent diabetes mellitus (NIDDM) is a metabolic disease associated with abnormal insulin secretion, the underlying mechanisms of which are unknown. Glucose-dependent signal transduction pathways were investigated in pancreatic islets derived from the db/db mouse, an animal model of NIDDM. After stimulation with glucose (4-12 mM), the changes in intracellular Ca2+ concentration ([Ca2+]i) were different; unlike control islets, db/db islets lacked an initial reduction of [Ca2+]i and the subsequent [Ca2+]i oscillations following stimulation with 12 mM glucose.

Thapsigargin inhibits the glucose-induced decrease of intracellular Ca2+ in mouse islets of Langerhans.

Stimulation of pancreatic islets of Langerhans with glucose results in changes in intracellular Ca2+ concentration ([Ca2+]i). With the use of mouse islets loaded with fura 2, the earliest glucose-induced alteration of [Ca2+]i was a pronounced decline in [Ca2+]i. This effect (phase 0) was evident 1 min after increasing extracellular glucose from 2 to 12 mM and was sustained for 3-5 min.

Endoplasmic reticulum calcium store regulates membrane potential in mouse islet beta-cells.

Glucose stimulation of islet beta-cell insulin secretion is initiated by membrane depolarization and an elevation in intracellular free calcium concentration ([Ca2+]i) from a combination of influx through depolarization-activated Ca2+ channels and intracellular Ca2+ store release. Prevention of Ca2+ store refilling with thapsigargin produced a sustained depolarization, leading to enhanced Ca2+ influx and an elevation in [Ca2+]i in 12 mM glucose. Depletion of intracellular Ca2+ stores by external EGTA reduced [Ca2+]i and also caused a long-lasting depolarization.

Dependence on NADH produced during glycolysis for beta-cell glucose signaling.

An increase in cytosolic ATP following glucose metabolism by pancreatic beta-cells is the key signal initiating insulin secretion by causing blockade of ATP-dependent K+ channels (KATP). This induces membrane depolarization, leading to an elevation in cytosolic Ca2+ ([Ca2+]i) and insulin secretion. In this report we identify the critical metabolic step by which glucose initiates changes in beta-cell KATP channel activity, membrane potential, and [Ca2+]i.

Amylin modulates beta-cell glucose sensing via effects on stimulus-secretion coupling.

The release of insulin from the pancreatic beta cell is dependent upon a complex interplay between stimulators and inhibitors. Recently, amylin, a peptide secreted by pancreatic beta cells, has been implicated in the development of type II (noninsulin dependent) diabetes through its modulation of the peripheral effects of insulin. However, the effect of amylin on insulin secretion from the beta cell has remained controversial.

Voltage-dependent intracellular calcium release from mouse islets stimulated by glucose.

Glucose-activated beta-cell insulin secretion depends upon elevation of intracellular calcium concentration, [Ca2+]i, which is thought to arise from Ca2+ influx through voltage-dependent calcium channels. Using fura-2-loaded mouse islets, we demonstrate, in fact, that the major component of the glucose-activated [Ca2+]i rise represents voltage-dependent intracellular Ca2+ release. Furthermore, the Ca2+ release pool possesses a novel pharmacology in that it is caffeine-sensitive but ryanodine-insensitive.

Calcium current regulation of depolarization-evoked calcium transients in beta-cells (HIT-T15).

Glucose-induced insulin secretion by beta-cells is linked to phasic increases in intracellular Ca2+ concentration ([Ca2+]i) arising from membrane depolarization. We examined the source of this Ca2+ in cultured beta-cells using rapid dual-wavelength spectroscopy of fura-2 under voltage-clamp conditions. Depolarization of the beta-cell initiated a sustained rise in [Ca2+]i that was dependent on the activation of L-type Ca2+ current that exhibited very slow inactivation.

Use of hydroxyurea in chronic myeloid leukemia during pregnancy: a case report.

The concomitant occurrence of pregnancy and chronic myeloid leukemia is uncommon. The use of hydroxyurea in chronic myeloid leukemia during pregnancy is unknown. We report on a patient with chronic myeloid leukemia in whom hydroxyurea was used during pregnancy with a successful outcome for both mother and fetus.

Divalent cations modulate the transient outward current in rat ventricular myocytes.

The modulation of the transient outward K+ current (Ito) by divalent cations was studied in enzymatically isolated rat ventricular myocytes with the whole cell patch-clamp technique. At holding potentials negative to -70 mV, 1 mM Cd2+ suppressed Ito, whereas, at potentials positive to -50 mV, the current was augmented. These effects were caused by shifts in the voltage dependence of both activation and inactivation of Ito toward more positive potentials.