Membrane depolarization induced by transcellular osmosis in internodal cells ofNitella flexilis

To assess the functional significance of late inspiratory (late-I) neurons in inspiratory off-switching (IOS), membrane potential and discharge properties were examined in vagotomized, decerebrate cats. During spontaneous IOS, late-I neurons displayed large membrane depolarization and associated discharge of action potentials that started in late inspiration, peaked at the end of inspiration, and ended during postinspiration. Depolarization was decreased by iontophoresis of dizocilpine and eliminated by tetrodotoxin. Stimulation of the vagus nerve or the nucleus parabrachialis medialis (NPBM) also evoked depolarization of late-I neurons and IOS. Waves of spontaneous chloride-dependent inhibitory postsynaptic potentials (IPSPs) preceded membrane depolarization during early inspiration and followed during postinspiration and stage 2 expiration of the respiratory cycle. Iontophoresed bicuculline depressed the IPSPs. Intravenous dizocilpine caused a greatly prolonged inspiratory discharge of the phrenic nerve (apneusis) and suppressed late-inspiratory depolarization as well as early-inspiratory IPSPs, resulting in a small constant depolarization throughout the apneusis. NPBM or vagal stimulation after dizocilpine produced small, stimulus-locked excitatory postsynaptic potentials (EPSPs) in late-I neurons. Neurobiotin-labeled late-I neurons revealed immunoreactivity for glutamic acid decarboxylase as well as N-methyl-d-aspartate (NMDA) receptors. These results suggest that late-I neurons are GABAergic inhibitory neurons, while the effects of bicuculline and dizocilpine indicate that they receive periodic waves of GABAergic IPSPs and glutamatergic EPSPs. The data lead to the conclusion that late-I neurons play an important inhibitory role in IOS. NMDA receptors are assumed to augment and/or synchronize late-inspiratory depolarization and discharge of late-I neurons, leading to GABA release and consequently off-switching of bulbar inspiratory neurons and phrenic motoneurons.

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Time-correlation between membrane depolarization and intracellular calcium in insulin secreting BRIN-BD11 cells: studies using FLIPR

Cell Calcium ◽

10.1016/j.ceca.2003.11.007 ◽

2004 ◽

Vol 36 (1) ◽

pp. 43-50 ◽

Cited By ~ 29

Author(s):

João C Miguel ◽

Steven Patterson ◽

Yasser H.A Abdel-Wahab ◽

Paulo C.F Mathias ◽

Peter R Flatt

Keyword(s):

Intracellular Calcium ◽

Time Correlation ◽

Membrane Depolarization

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Impaired Insulin Secretion by Diphenyleneiodium Associated with Perturbation of Cytosolic Ca2+ Dynamics in Pancreatic β-Cells

Endocrinology ◽

10.1210/en.2008-0186 ◽

2008 ◽

Vol 149 (11) ◽

pp. 5391-5400 ◽

Cited By ~ 22

Author(s):

Hirofumi Imoto ◽

Nobuhiro Sasaki ◽

Masanori Iwase ◽

Udai Nakamura ◽

Miwako Oku ◽

...

Keyword(s):

Insulin Secretion ◽

Nadph Oxidase ◽

Nicotinamide Adenine Dinucleotide Phosphate ◽

Mitochondrial Respiratory Chain ◽

Membrane Depolarization ◽

Oxidase Inhibitor ◽

Channel Blockers ◽

Β Cells ◽

Impaired Insulin Secretion ◽

Impaired Insulin

Pancreatic islets express the superoxide-producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, but its role remains unknown. To address this, we studied the mechanisms of impaired insulin secretion induced by diphenyleneiodium (DPI), an NADPH oxidase inhibitor. We investigated the effects of DPI on glucose- and nonfuel-stimulated insulin secretion, islet glucose metabolism, and intracellular Ca2+ concentration ([Ca2+]i) dynamics in rat islets and β-cell line RINm5F cells. DPI did not affect insulin secretion at 3.3 mm glucose but totally suppressed insulin secretion stimulated by 16.7 mm glucose (percentage of control, 9.2 ± 1.2%; P <0.001). DPI also inhibited insulin release by high K+-induced membrane depolarization (percentage of control, 36.0 ± 5.3%; P <0.01) and protein kinase C activation (percentage of control, 30.2 ± 10.6% in the presence of extracellular Ca2+, P <0.01; percentage of control, 42.0 ± 4.7% in the absence of extracellular Ca2+, P <0.01). However, DPI had no effect on mastoparan-induced insulin secretion at 3.3 and 16.7 mm glucose under Ca2+-free conditions. DPI significantly suppressed islet glucose oxidation and ATP content through its known inhibitory action on complex I in the mitochondrial respiratory chain. On the other hand, DPI altered [Ca2+]i dynamics in response to high glucose and membrane depolarization, and DPI per se dose-dependently increased [Ca2+]i. The DPI-induced [Ca2+]i rise was associated with a transient increase in insulin secretion and was attenuated by removal of extracellular Ca2+, by L-type voltage-dependent Ca2+ channel blockers, by mitochondrial inhibitors, or by addition of 0.1 or 1.0 μm H2O2 exogenously. Our results showed that DPI impairment of insulin secretion involved altered Ca2+ signaling, suggesting that NADPH oxidase may modulate Ca2+ signaling in β-cells.

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