Characterization of Ca2+‐activated 86Rb+ fluxes in rat C6 glioma cells: a system for identifying novel IKCa‐channel toxins

De-Allie, F.A; Bolsover, Steven; Nowicky, Alexander V.; Strong, Peter

doi:10.1111/j.1476-5381.1996.tb15215.x

Cited by 18 publications

(10 citation statements)

References 56 publications

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“…Consequently, the open probability of voltage-dependent K + and Clchannels should be very small at resting potentials of -50 and -70 mV. Evidence for CTX-sensitive, Ca 2+ -activated K + channels was found in a study investigating the effects of a Ca 2+ ionophore on C6 cells [2]. Moreover, we measured resting potentials less negative with (-61 mV) than without (-71 mV) EGTA in the pipette solution, suggesting that Ca 2+ -activated K + channels are active at rest.…”

Section: Discussionmentioning

confidence: 96%

Control of cell proliferation by cell volume alterations in rat C6 glioma cells

Rouzaire‐Dubois

Milandri

Bostel

et al. 2000

Pflugers Arch - Eur J Physiol

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K+ and Cl- channels are involved in regulating the proliferation of a number of cell types. Two main hypotheses have been proposed to explain the mechanism by which these channels influence cell proliferation: regulation of membrane potential and regulation of cell volume. In order to test these hypotheses, we measured, under different experimental conditions, the volume, membrane potential and rate of proliferation of C6 glioma cells. Cells cultured in control medium for 1-4 days were compared with cells cultured for the same period of time in the presence of broad spectrum channel blockers: tetraethylammonium, 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and Cs+, in hypertonic media (29% increased osmolarity with NaCl, KCl or sucrose), in hypotonic medium (23% decreased osmolarity with H2O) or in the presence of the specific channel blockers, i.e. mast cell degranulating peptide, charybdotoxin or chlorotoxin. In all of these conditions, we observed a close correspondence between the rate of proliferation and the mean cell volume. The proliferation decreased when volume increased. Moreover, whereas control cells were flattened, spindle-shaped, bipolar or multipolar, cells cultured in media supplemented with NPPB, KCl or CsCl were round with few processes. Of the agents tested, only KCl and Cs+ depolarized the cells. These results show that alterations of the rate of proliferation by K+ and Cl- channel blockers or anisotonia are closely related with changes in cell volume or form but are not correlated with changes in membrane potential.

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Section: Discussionmentioning

confidence: 96%

Control of cell proliferation by cell volume alterations in rat C6 glioma cells

Rouzaire‐Dubois

Milandri

Bostel

et al. 2000

Pflugers Arch - Eur J Physiol

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“…It is blocked by charybdotoxin (CTX) but not the structurally related peptide iberiotoxin (IBX), both of which block BK channels (10). Apamin, a potent blocker of certain native (11,12) and cloned (5) SK channels, does not block IK channels (13). The Gardos channel is also blocked by some imidazole compounds, such as clotrimazole, but not ketoconazole (ref.…”

mentioning

confidence: 99%

A human intermediate conductance calcium-activated potassium channel

Ishii

Silvia

Hirschberg

et al. 1997

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

558

491

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An intermediate conductance calciumactivated potassium channel, hIK1, was cloned from human pancreas. The predicted amino acid sequence is related to, but distinct from, the small conductance calcium-activated potassium channel subfamily, which is Ϸ50% conserved. hIK1 mRNA was detected in peripheral tissues but not in brain. Expression of hIK1 in Xenopus oocytes gave rise to inwardly rectifying potassium currents, which were activated by submicromolar concentrations of intracellular calcium (K 0.5 ‫؍‬ 0.3 M). Although the K 0.5 for calcium was similar to that of small conductance calcium-activated potassium channels, the slope factor derived from the Hill equation was significantly reduced (1.7 vs. 3.5). Single-channel current amplitudes ref lected the macroscopic inward rectification and revealed a conductance level of 39 pS in the inward direction. hIK1 currents were reversibly blocked by charybdotoxin (K i ‫؍‬ 2.5 nM) and clotrimazole (K i ‫؍‬ 24.8 nM) but were minimally affected by apamin (100 nM), iberiotoxin (50 nM), or ketoconazole (10 M). These biophysical and pharmacological properties are consistent with native intermediate conductance calcium-activated potassium channels, including the erythrocyte Gardos channel.

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“…LQH and ChTX, the active toxin extracted from LQH, strongly inhibit ATPstimulated 86 Rb + efflux from cultured pituicytes. ChTX is a blocker of several types of K + channel [17], including intermediate-conductance K Ca channels [6], largeconductance K Ca channels [9] and also the voltage-dependent K + channels (Kv) [25].…”

Section: Discussionmentioning

confidence: 99%

Potassium efflux triggered by P2Y purinoceptor activation in cultured pituicytes

Troadec

Thirion

Petturiti

et al. 2000

Pflugers Arch - Eur J Physiol

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We have previously investigated the effects of extracellular ATP on the concentration of free cytosolic calcium ([Ca2+]i) from rat cultured neurohypophysial astrocytes (pituicytes). We demonstrated that ATP acts via a P2Y receptor to increase [Ca2+]i. In the present study, we examine the effect of ATP on K+ efflux using 86Rb+ as an isotopic tracer, in order to characterize the possible presence of a Ca2+-activated K+ conductance and to establish the implications of pituicytes in the regulation of stimulus-secretion coupling. ATP evoked an increase in 86Rb+ efflux from cultured pituicytes. This effect was Ca2+ dependent, as indicated by the unresponsiveness of cells loaded with BAPTA/AM (20 microM). Furthermore, the effect of ATP was mimicked by 2-methylthio-adenosine-5'-triphosphate (2MeSATP), a P2 purinoceptor agonist, and abolished by Reactive Blue 2 (RB-2), a selective P2Y antagonist, implying a role for the P2Y purinoreceptor. A pharmacological study revealed that Ba2+ and tetraethylammonium (TEA), two inhibitors of K+ channels, both strongly reduced the ATP-stimulated 86Rb+ efflux. In addition, the effect of ATP was modulated by different peptidic toxins. Apamin (100 nM), an inhibitor of the small-conductance Ca2+-activated K+ channels, partly blocked ATP-induced 86Rb+ efflux. Leiurus quinquestriatus hebraeus (LQH) scorpion venom (20 microg/ml) and Buthus tamulus (BT) scorpion venom (20-200 microg/ml) inhibited ATP-induced 86Rb+ efflux. The specificity of the effects of the crude venoms was checked using charybdotoxin (100 nM) and iberiotoxin (1 pM), which are the active toxins extracted from the LQH and BT venoms, respectively. These data indicate the involvement of several types of Ca2+-activated K+ channels in the ATP-dependent K+ efflux, and lead to the proposal that, in the neurohypophysis, extracellular ATP released by nerve terminals may act directly on the pituicytes and induce a K+ efflux via a P2Y purinoreceptor.

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Characterization of Ca²⁺‐activated ⁸⁶Rb⁺ fluxes in rat C6 glioma cells: a system for identifying novel IK_Ca‐channel toxins

Abstract: 1 The pharmacological characteristics of a putative Ca2" activated K+ channel (IKCa channel)

Cited by 18 publications

References 56 publications

Control of cell proliferation by cell volume alterations in rat C6 glioma cells

Control of cell proliferation by cell volume alterations in rat C6 glioma cells

A human intermediate conductance calcium-activated potassium channel

Potassium efflux triggered by P2Y purinoceptor activation in cultured pituicytes

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