The inactivating K+ current in GH3 pituitary cells and its modification by chemical reagents.

Oxford, Gerry S.; Wagoner, P. Kay

doi:10.1113/jphysiol.1989.sp017550

Cited by 81 publications

(74 citation statements)

References 56 publications

(71 reference statements)

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“…Except in immunoblot experiments, amylin and bovine serum albumin (0.5 mg/ml) were dissolved into the external recording solution immediately prior to application to single cells via a U-tube (11). Amylin can precipitate from solution and adheres avidly to both plastics and glass, thus actual concentrations of the delivered peptide are likely lower than those reported.…”

Section: Methodsmentioning

confidence: 99%

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

Wagoner

Chen

Worley

et al. 1993

Proc. Natl. Acad. Sci. U.S.A.

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The release of insulin from the pancreatic ,B cell is dependent upon a complex interplay between stinulators and inhibitors. Recently, amylin, a peptide secreted by pancreatic ,B ceils, 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 .8 cell has remained controversial.It is reported here that in single ,B cells exhibiting normal glucose sensing, amylin causes membrane hyperpolarization, increases in net outward current, and reductions in insulin secretion. In contrast, in cells with abnormal glucose sensing (e.g., from db/db diabetic mice), amylin has no effect on electrical activity or secretion. Thus, amylin's effects on excitation-secretion coupling in the (8 cell of the pancreas appear to be linked to the cell's capacity for normal glucose sensing.Although the mysteries underlying the effects of glucose and other secretagogues on pancreatic ,B-cell electrical and secretory activity are rapidly unfolding, the mechanisms by which hormones and peptides modulate these activities remain unclear. Certain neuropeptides, released by nerves supplying the pancreas, decrease insulin secretion. This inhibition involves coupling between receptors and ion channels (1). In contrast to such neurotransmitters, it is not known whether and how peptides secreted from the ,B cells themselves affect insulin secretion. Amylin, a 37-aa peptide, is colocalized with insulin in 13-cell secretory granules of human islets (2) and is cosecreted with insulin. It is also the major component of pancreatic islet amyloid commonly found in the pancreases of patients with non-insulin-dependent diabetes mellitus (3). In this disease, loss of normal glucose sensing is one of the earliest defects. Although peripheral actions of amylin have been demonstrated, the influence of amylin on insulin secretion is still debated (4-7). Though the overall role ofamylin in regulating insulin secretion and in the development of diabetes may remain unclear for some time, it is critical to determine the effects of amylin on stimulussecretion coupling at the single-cell level. Thus, we have examined the effects of amylin on excitation and insulin secretion in single isolated pancreatic /3 cells that exhibit normal or abnormal glucose sensing. METHODSTo determine the effects of both glucose and amylin on membrane electrical parameters of single /8 cells, we used the nystatin perforated patch technique (8) to record membrane potentials and ion currents. Detection of insulin secretion from single 13 cells was accomplished using a sequential-cell immunoblot method (9) whereby cells are stimulated to secrete insulin into peptide-retentive immunoblot materialThe 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 solely to indicate this fact. and secreted hormone is quantified by standar...

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Section: Methodsmentioning

confidence: 99%

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

Wagoner

Chen

Worley

et al. 1993

Proc. Natl. Acad. Sci. U.S.A.

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“…Its effects on ionic channels have not been widely explored, but it is known that similar agents are capable of slowing down the inactivation of the Na¤ current (Ulbricht, 1990). We chose IAA because it did not affect the inactivation properties of K¤ currents in the experiments performed by Oxford & Wagoner (1989). When added to the pipette solution, we found that IAA increased the INa,p in neocortical neurones, without inducing a large shift in the voltage dependence of current activation.…”

Section: Effects Of Other Agents Acting On Na¤ Current Inactivationmentioning

confidence: 99%

Anemone toxin (ATX II)‐induced increase in persistent sodium current: effects on the firing properties of rat neocortical pyramidal neurones

Mantegazza

Franceschetti

Avanzini

1998

The Journal of Physiology

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The experiments were performed on sensorimotor cortex using current‐clamp intracellular recordings in layer V pyramidal neurones and whole‐cell voltage‐clamp recordings in dissociated pyramidal neurones. The intracellularly recorded neurones were classified on the basis of their firing characteristics as intrinsically bursting (IB) and regular spiking (RS). The RS neurones were further subdivided into adapting (RSAD) or non‐adapting (RSNA), depending on the presence or absence of spike frequency adaptation. Since burst firing in neocortical pyramidal neurones has previously been suggested to depend on the persistent fraction of Na+ current (INa,p), pharmacological manipulations with drugs affecting INa inactivation have been employed. ATX II, a toxin derived from Anemonia sulcata, selectively inhibited INa fast inactivation in dissociated neurones. In current‐clamp experiments on neocortical slices, ATX II enhanced the naturally occurring burst firing in IB neurones and revealed the ability of RSNA neurones to discharge in bursts, whereas in RSAD neurones it increased firing frequency, without inducing burst discharges. During the ATX II effect, in all the three neuronal subclasses, episodes of a metastable condition occurred, characterized by long‐lasting depolarizing shifts, triggered by action potentials, which were attributed to a peak in the toxin‐induced inhibition of INa inactivation. The ATX II effect on IB and RSNA neurones was compared with that induced by veratridine and iodoacetamide. Veratridine induced a small increase in the INa and a large shift to the left in the voltage dependence of INa activation. Accordingly, its major effect on firing characteristics was the induction of prolonged tonic discharges, associated with burst facilitation less pronounced than that induced by ATX II. The alkylating agent iodoacetamide was able to induce a selective small increase in the INa,p, with a similar but less pronounced effect than ATX II on firing behaviour. The present results show that pharmacological manipulations capable of slowing down INa inactivation significantly enhance burst behaviour in IB neurones and promote burst firing in otherwise non‐bursting RSNA neurones. We suggest that IB and, to a lesser extent, RSNA neurones are endowed with a relatively large fraction of INa,p which, in physiological conditions, is sufficient to sustain bursting in IB but not in RSNA neurones.

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“…Under such conditions, two types of K+ current can be observed in GH, cells: first, a voltage-dependent inactivating current sensitive to 4-aminopyridine (4-AP, Dubinsky and Oxford, 1984;Oxford and Wagoner, 1989) and second, a noninactivating, voltage-activated current that is at least partially blocked by 5 mM TEA (Oxford and Wagoner, 1989). Some evidence supports the view that this current reflects Ca2+-activated K+ current activated by voltage in the absence of Ca*+ (Oxford and Wagoner, 1989). However, at present, some contribution of a delayed-rectifier type of K+ channel cannot be excluded.…”

Section: Concentration Dependence Of Blockade Of Ca2+ Current By Halomentioning

confidence: 99%

Halothane inhibits two components of calcium current in clonal (GH3) pituitary cells

et al. 1991

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The effect of halothane on isolated calcium (Ca2+) current of clonal (GH3) pituitary cells was investigated using standard whole-cell clamp techniques at room temperature. Halothane (0.1–5.0 mM) reversibly reduced both the low-threshold, transient [low-voltage-activated (LVA)] component and the high-threshold [high-voltage-activated (HVA)] component of Ca2+ current. Halothane had little effect on the voltage dependence of activation or inactivation of either component of Ca2+ current. Inhibition of the peak high-threshold Ca2+ current was half- maximal at about 0.8 mM halothane, with maximal inhibition (100%) occurring with 5 mM halothane. When measured at the end of a 190-msec command step, half-maximal reduction of high-threshold current occurred at less than 0.5 mM halothane. The low-threshold transient current was less sensitive to halothane, with half-maximal inhibition of peak transient current activated at -30 mV occurring at approximately 1.3 mM. The effect of halothane on the HVA current was apparently not mediated by changes in intracellular Ca2+ concentration. The ability of halothane to inhibit Ca2+ current was unaffected by either the inclusion of the rapid Ca2+ buffer 1,2-bis(2-aminophenoxy)ethane N,N,N′,N′-tetraacetic acid (BAPTA) in the recording pipette or exposure of the cell to 10 mM caffeine. To assess the selectivity of the effect of halothane, the actions of halothane on two components of voltage- activated potassium (K+) current observed in the absence of extracellular Ca2+ and on voltage-dependent sodium (Na+) current were also examined. Halothane had no effect on the voltage-dependent, inactivating K+ current of GH3 cells at concentrations up to 1.2 mM. In contrast, the non-inactivating K+ current, though less sensitive to halothane than either Ca2+ current, was reduced by about 40% by 1.2 mM halothane at +20 mV. Peak Na+ current was also blocked by halothane, but 50% block required around 2.6 mM halothane with little effect at 1.6 mM. Reduction of Na+ current was associated with a substantial negative shift in the steady-state inactivation curve. Although the results indicate that a number of voltage-dependent ionic currents are sensitive to halothane, both components of Ca2+ current exhibit a greater sensitivity to halothane than any of three other voltage- dependent currents in GH3 cells. These results show that GH3 cell Ca2+ currents are selectively inhibited by clinically appropriate concentrations of halothane and that the reduction of Ca2+ current can account for the inhibition by halothane of TRH- or KCl-induced prolactin secretion in GH3 cells.

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The inactivating K+ current in GH3 pituitary cells and its modification by chemical reagents.

Cited by 81 publications

References 56 publications

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

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

Anemone toxin (ATX II)‐induced increase in persistent sodium current: effects on the firing properties of rat neocortical pyramidal neurones

Halothane inhibits two components of calcium current in clonal (GH3) pituitary cells

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