Studies of calcium-dependent ionic currents and their muscarinic regulation in pancreatic insulin-secreting cells.
Item
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Title
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Studies of calcium-dependent ionic currents and their muscarinic regulation in pancreatic insulin-secreting cells.
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Identifier
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AAI9820551
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identifier
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9820551
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Creator
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Kozak, Juliusz Ashot.
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Contributor
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Adviser: Diomedes E. Logothetis
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Animal Physiology | Biophysics, General | Biology, Cell
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Abstract
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Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent Cl{dollar}\sp-{dollar} and K{dollar}\sp+{dollar} currents were characterized in insulin-secreting {dollar}\beta{dollar}TC-3 cells using perforated-patch whole cell recording technique. Both Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent currents were found to be activated by depolarizing voltage steps which allowed influx of Ca{dollar}\sp{lcub}2+{rcub}{dollar} through the Ca{dollar}\sp{lcub}2+{rcub}{dollar} channels. The Ca{dollar}\sp{lcub}2+{rcub}{dollar} channels in {dollar}\beta{dollar}TC-3 cells were also described and found to belong to the L-type family based on its kinetic and pharmacological properties, similar to those found in native {dollar}\beta{dollar} cells. The Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent currents activated slowly and had characteristic tail currents revealed upon repolarization. The Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent chloride current reversal potential was sensitive to changes in Cl{dollar}\sp-{dollar} concentrations in the bathing solution and {dollar}\rm Br\sp-,\ NO\sb3\sp-,\ I\sp-{dollar} and acetate were permeant anions in addition to Cl{dollar}\sp-.{dollar} Niflumic acid and DIDS were effective blockers of this current at high micromolar concentrations. The Cl{dollar}\sp-{dollar} ion equilibrium potential was found to be close to {dollar}-{dollar}22 mV under conditions where the internal Cl{dollar}\sp-{dollar} concentration was undisturbed. Both Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent currents could also be activated if Ca{dollar}\sp{lcub}2+{rcub}{dollar} in the extracellular medium was substituted with Sr{dollar}\sp{lcub}2+{rcub}.{dollar} Ba{dollar}\sp{lcub}2+{rcub},{dollar} however was not effective in activating these currents. The Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent K{dollar}\sp+{dollar} current exhibited unique pharmacological properties: it was sensitive to block by charybdotoxin and clotrimazole and quinine but not tetraethylammonium, apamin, iberiotoxin, scyllatoxin and kaliotoxin. This current was found to be activated by niflumic acid. The Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent K{dollar}\sp+{dollar} channels were permeable to Tl{dollar}\sp+,{dollar} Rb{dollar}\sp+{dollar} and NH{dollar}\sb4\sp+{dollar} but not to Cs{dollar}\sp+{dollar} and Na{dollar}\sp+.{dollar} A current which was Ca{dollar}\sp{lcub}2+{rcub}{dollar}-dependent and displayed kinetics similar to the {dollar}\beta{dollar}TC-3 K{dollar}\sp+{dollar} current was present in porcine islet cells. It was blocked by quinidine but was insensitive to charybdotoxin.;Muscarinic stimulation of the {dollar}\beta{dollar}TC-3 cells was capable of activating both Ca{dollar}\sp{lcub}2+{rcub}{dollar} dependent currents in the presence or absence of external Ca{dollar}\sp{lcub}2+{rcub},{dollar} presumably by releasing Ca{dollar}\sp{lcub}2+{rcub}{dollar} from internal stores. Both currents, when activated by muscarinic agonists often displayed time dependent oscillations. Thus, the ionic mechanism underlying muscarinic regulation of the insulin secreting cells has been described.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
