Effects of [Ca2+]i and temperature on minK channels expressed in Xenopus oocytes

Büsch, Andreas; Läng, Florian

doi:10.1016/0014-5793(93)81715-c

Cited by 38 publications

(18 citation statements)

References 16 publications

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“…However, previous findings for transfected COS and Chinese hamster ovary cells as well as Xenopus oocytes (4,5,15) showed that the channel regulator not only affected activation kinetics (as with our cells) but also markedly increased its density. Differences in experimental procedures may account for this discrepancy, particularly with Xenopus oocytes in which IsK-induced Kv-LQT1 current is highly temperature-dependent (16). Previous experiments were performed at 20 -22°C, whereas in our study a physiological temperature (37°C) was chosen.…”

Section: Without and With Iskmentioning

confidence: 81%

A Dominant Negative Isoform of the Long QT Syndrome 1 Gene Product

Demolombe

Baró

Péreón

et al. 1998

Journal of Biological Chemistry

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Section: Without and With Iskmentioning

confidence: 81%

A Dominant Negative Isoform of the Long QT Syndrome 1 Gene Product

Demolombe

Baró

Péreón

et al. 1998

Journal of Biological Chemistry

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“…I Ks in Xenopus laevis oocytes is strongly temperaturedependent [7]. Since the interaction of KCNE1 with KCNQ1 was not known at that time, the temperature dependence of KCNQ1 homomers has not been investigated so far.…”

Section: Resultsmentioning

confidence: 99%

“…This strong temperature dependence and the sigmoidal activation time course of I Ks probably reflect the complex gating mechanism of the corresponding channel complex. Since a conformational change within a preformed channel molecule is not expected to be that temperature sensitive [7] it has been proposed that KCNQ1 and KCNE1 subunits coassemble during a depolarising voltage step. This hypothesis could explain the slower activation kinetics at a lower temperature by the higher rigidity of the membrane lipids and proteins at this temperature.…”

Section: Discussionmentioning

confidence: 99%

KCNE1 reverses the response of the human K + channel KCNQ1 to cytosolic pH changes and alters its pharmacology and sensitivity to temperature

Unsöld

Kerst

Brousos

et al. 2000

Pfl�gers Archiv European Journal of Physiology

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Previous studies have shown that heteromultimeric KCNQ1/KCNE1 (KvLQT1/minK) channels and homomultimeric KCNQ1 (KvLQT1) channels exhibit different current properties, e.g. distinct kinetics and different sensitivities to drugs. In this study we report on the divergent responses to internal pH changes and further characterize some of the current properties of the human isoforms of KCNQ1 and KCNE1 expressed in Chinese hamster ovary (CHO) cells or Xenopus laevis oocytes. Decreasing the bath temperature from 37 degrees C to 20 degrees C increased the half-activation time by a factor of 5 for KCNQ1/KCNE1 currents (IKs) but by only twofold (not significant) for KCNQ1 currents (IK) in CHO cells. Acidification of cytosolic pH (pHi) increased IKs but decreased 1K whereas intracellular alkalinization decreased I(Ks) but increased IK. pHi-induced changes in intracellular Ca2+ activity ([Ca2+]i) did not correlate with the current responses. At 20 degrees C mefenamic acid (0.1 mM) significantly augmented IKs but slightly decreased IK. It changed the slow activation kinetics of I(Ks) to an instantaneous onset. The form of the current/voltage (I/V) curve changed from sigmoidal to almost linear. In contrast, at 37 degrees C, mefenamic acid also increased I(Ks) but slowed the activation kinetics and shifted the voltage activation to more hyperpolarized values without markedly affecting the sigmoidal shape of the I/V curve. The potassium channel blockers clotrimazole and tetrapentylammonium (TPeA) inhibited I(Ks) with a lower potency than I(K). These results show that coexpression of KCNE1 reversed pH regulation of KCNQ1 from inhibition to activation by acidic pHi. In addition, KCNE1 altered the pharmacological properties and sensitivity to temperature of KCNQ1. The pH-dependence of I(Ks) might be of clinical and pathophysiological relevance in the pathogenesis of ischaemic cardiac arrhythmias.

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“…Attempts to resolve I Ks and min K single channels have been equally unsuccessful resulting instead in the recording of a macropatch current with no visible single channels in both guineapig ventricle and Xenopus oocytes Yang and Sigworth 1995). I sK and I Ks are both regulated in the same way by protein kinase A (PKA) and by calcium: I sK is enhanced by raised intracellular calcium (Busch et al 1992;Busch and Lang 1993) and activation of PKA enhanced I sK (Blumenthal and Kaczmarek 1992), increased total guinea-pig I K in the heart (Tohse et al 1987;Tohse 1990; and selectively enhanced cardiac I Ks (Sanguinetti et al 1991;Busch and Maylie 1993).…”

Section: Introductionmentioning

confidence: 99%

Block by propofol and thiopentone of the min K current (IsK) expressed in Xenopus oocytes

Heath¹,

Terrar²

1997

Naunyn-Schmiedeberg's Arch Pharmacol

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The slowly activating component of the delayed rectifier potassium current (I(Ks)) in the heart is important during the repolarization of the cardiac action potential. Injection into Xenopus oocytes of mRNA coding for the min K protein induces a similar current (IsK) and recent observations support the hypothesis that functional channels result from the association of the min K protein with an endogenous K+ channel similar to the recently cloned KvLQT1. The general anaesthetics propofol and thiopentone have been shown to suppress cardiac I(Ks) with no effect on the rapidly activating component of I(K) (Takahashi and Terrar 1995). It was therefore of interest to test whether IsK was also inhibited by propofol and thiopentone. IsK was induced following injection into oocytes of min K mRNA which was transcribed in vitro from a synthetic gene (Hausdorff et al. 1991). IsK was activated by step depolarizations to a series of potentials from a holding potential of -40 mV and measured as the deactivating tail current on repolarization to the holding potential. Following a 2 s depolarization to +45 mV, propofol and thiopentone caused concentration-dependent reductions in IsK. The estimated IC50 value for the block of IsK by propofol was 250 microM and by thiopentone was 56 microM. Block of IsK by both propofol and thiopentone was not dependent on voltage or time. The reductions in IsK caused by propofol and thiopentone are consistent with the previously reported effects of these anaesthetics on I(Ks) in the heart and support the hypothesis that the min K protein contributes to the molecular basis of the cardiac I(Ks) channel.

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Effects of [Ca²⁺]_i and temperature on minK channels expressed in Xenopus oocytes

Cited by 38 publications

References 16 publications

A Dominant Negative Isoform of the Long QT Syndrome 1 Gene Product

A Dominant Negative Isoform of the Long QT Syndrome 1 Gene Product

KCNE1 reverses the response of the human K + channel KCNQ1 to cytosolic pH changes and alters its pharmacology and sensitivity to temperature

Block by propofol and thiopentone of the min K current (IsK) expressed in Xenopus oocytes

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