scholarly journals The effects of membrane potential on active and passive sodium transport in Xenopus oocytes.

1987 ◽  
Vol 385 (1) ◽  
pp. 643-659 ◽  
Author(s):  
D A Eisner ◽  
M Valdeolmillos ◽  
S Wray
Keyword(s):  
Membrane Potential ◽  
Sodium Transport ◽  
Xenopus Oocytes

scholarly journals Extracellular Hco3− Dependence of Electrogenic Na/Hco3 Cotransporters Cloned from Salamander and Rat Kidney

2000 ◽  
Vol 115 (5) ◽  
pp. 533-546 ◽  
Author(s):  
Irina I. Grichtchenko ◽  
Michael F. Romero ◽  
Walter F. Boron
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Xenopus Oocytes ◽  
Rat Kidney ◽  
Outward Current ◽  
Membrane Vesicles ◽  
Disulfonic Acid ◽  
Ambystoma Tigrinum ◽  
Ph Titration ◽  
Electrode Voltage

We studied the extracellular [HCOabstract 3 −] dependence of two renal clones of the electrogenic Na/HCO3 cotransporter (NBC) heterologously expressed in Xenopus oocytes. We used microelectrodes to measure the change in membrane potential (ΔVm) elicited by the NBC cloned from the kidney of the salamander Ambystoma tigrinum (akNBC) and by the NBC cloned from the kidney of rat (rkNBC). We used a two-electrode voltage clamp to measure the change in current (ΔI) elicited by rkNBC. Briefly exposing an NBC-expressing oocyte to HCOabstract 3 −/CO2 (0.33–99 mM HCOabstract 3−, pHo 7.5) elicited an immediate, DIDS (4,4-diisothiocyanatostilbene-2,2-disulfonic acid)-sensitive and Na+-dependent hyperpolarization (or outward current). In ΔVm experiments, the apparent Km for HCOabstract 3− of akNBC (10.6 mM) and rkNBC (10.8 mM) were similar. However, under voltage-clamp conditions, the apparent Km for HCOabstract 3− of rkNBC was less (6.5 mM). Because it has been reported that SOabstract 3=/HSO abstract 3− stimulates Na/HCO3 cotransport in renal membrane vesicles (a result that supports the existence of a COabstract 3= binding site with which SOabstract 3= interacts), we examined the effect of SOabstract 3=/HSO abstract 3− on rkNBC. In voltage-clamp studies, we found that neither 33 mM SOabstract 4= nor 33 mM SOabstract 3 =/HSOabstract 3− substantially affects the apparent Km for HCO abstract 3−. We also used microelectrodes to monitor intracellular pH (pHi) while exposing rkNBC-expressing oocytes to 3.3 mM HCOabstract 3 −/0.5% CO2. We found that SO abstract 3=/HSOabstract 3 − did not significantly affect the DIDS-sensitive component of the pHi recovery from the initial CO2 -induced acidification. We also monitored the rkNBC current while simultaneously varying [CO2]o, pHo, and [COabstract 3=]o at a fixed [HCOabstract 3−]o of 33 mM. A Michaelis-Menten equation poorly fitted the data expressed as current versus [COabstract 3=]o . However, a pH titration curve nicely fitted the data expressed as current versus pHo. Thus, rkNBC expressed in Xenopus oocytes does not appear to interact with SOabstract 3 =, HSOabstract 3−, or COabstract 3=.

scholarly journals Assessment of Intracellular Calcium and Plasmalemmal Membrane Potential in Cryopreserved Metaphase II Mouse Oocytes

2020 ◽  
Author(s):  
Omar Farhan Ammar ◽  
Therishnee Moodley
Keyword(s):  
Membrane Potential ◽  
Xenopus Oocytes ◽  
Channel Blocker ◽  
Oocyte Activation ◽  
Human Oocytes ◽  
Mouse Oocytes ◽  
Failed Fertilization ◽  
Intracellular Ca ◽  
In Vitro Ageing

Abstract Objectives: Ca2+ is critical for normal oocyte activation and fertilization, and any alteration to the Ca2+ homeostasis may lead to failed fertilization or even cell death. It has been shown that intracellular Ca2+ is increased in bovine and human oocytes when cultured in vitro. Additionally, ATP sensitive potassium channels have been characterised recently in human and Xenopus oocytes. Glibenclamide a KATP channel blocker was shown to protect human oocytes from Ca+2 overloading via inhibition of plasmalemmal KATP channels. This research note aims to demonstrate the effects of oxidative stress and in vitro ageing on the intracellular Ca+2 and plasmalemmal membrane potential dynamics in cryopreserved metaphase II (MII) mouse oocytes. Also, this study aims to show if glibenclamide (a KATP channel blocker ) has a role in regulating intracellular Ca+2 and plasmalemmal membrane potential through KATP channels in cryopreserved metaphase II mouse oocytes.Results: our data did not show an increase in intracellular Ca2+ in untreated cryopreserved mouse oocytes loaded with Fluo-3 AM dye. However, an increase in the plasmalemmal membrane potential was noticed (hyperpolarization). Glibenclamide has shown no significant effect on Ca2+ and plasmalemmal membrane potential.

Tetrabutylammonium induces a voltage-dependent block of kainate current in Xenopus oocytes injected with rat brain mRNA

1990 ◽  
Vol 68 (8) ◽  
pp. 1069-1078 ◽  
Author(s):  
John C. R. Randle
Keyword(s):  
Membrane Potential ◽  
Amino Acid ◽  
Xenopus Oocytes ◽  
Excitatory Amino Acid ◽  
Kainate Receptor ◽  
Induced Current ◽  
Excitatory Amino Acid Receptor ◽  
Acid Receptor ◽  
Cationic Current ◽  
Voltage Dependent

Following injection of rat striatal and cerebrellar mRNA, Xenopus oocytes were voltage clamped and current responses to the excitatory amino acid receptor agonist, kainate, were recorded. This nonspecific cationic current is carried principally by Na+ and K+ and reverses polarity at a membrane potential of approximately −5 mV. When the membrane potential was voltage clamped to −60 mV, bath-applied tetrabutylammonium (0.1–30 mM) produced a rapid, concentration dependent and reversible block of kainate-induced inward current with an IC50 of 1.3 mM. Tetraalkylammonium derivatives having shorter chains (methyl, ethyl, and propyl) were relatively ineffective blockers. Longer alkyl chain derivatives (pentyl, hexyl, and heptyl) were more potent than tetrabutylammonium but limited in their usefulness by their toxicity. The antagonism of kainate-induced current by tetrabutylammonium displayed apparently uncompetitive kinetics, in contrast with the competitive antagonism by γ-D-glutamylaminomethylsulfonate. The block by tetrabutylammonium was strongly voltage dependent; an e-fold change in IC50 was observed for a 27 mV change in holding potential. Replacement of the Na+ in the medium with a more permeant cation (NH4+), a less permeant cation (tetramethylammonium), or an uncharged solute (mannitol) had little effect on the block of kainate-induced current by tetrabutylammonium. The rates of association and dissociation of tetrabutylammonium with the kainate receptor–channel are clearly rapid. These observations suggest that tetrabutylammonium enters and blocks the kainate receptor-associated cation selective channel. Tetrabutylammonium appears to traverse 80–90% of the membrane electrical field to reach a relatively low-affinity binding site that may simply be a narrowing of the channel.Key words: voltage clamp, excitatory amino acid receptor, neurotransmitter-activated ionic currents, striatum, cerebellum.

scholarly journals Action potentials in Xenopus oocytes triggered by blue light

2020 ◽  
Vol 152 (5) ◽  
Author(s):  
Florian Walther ◽  
Dominic Feind ◽  
Christian vom Dahl ◽  
Christoph Emanuel Müller ◽  
Taulant Kukaj ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Blue Light ◽  
Action Potentials ◽  
Xenopus Oocytes ◽  
Na Channel ◽  
Xenopus Laevis Oocytes ◽  
Na Channels ◽  
Excitable Cells ◽  
Voltage Gated

Voltage-gated sodium (Na+) channels are responsible for the fast upstroke of the action potential of excitable cells. The different α subunits of Na+ channels respond to brief membrane depolarizations above a threshold level by undergoing conformational changes that result in the opening of the pore and a subsequent inward flux of Na+. Physiologically, these initial membrane depolarizations are caused by other ion channels that are activated by a variety of stimuli such as mechanical stretch, temperature changes, and various ligands. In the present study, we developed an optogenetic approach to activate Na+ channels and elicit action potentials in Xenopus laevis oocytes. All recordings were performed by the two-microelectrode technique. We first coupled channelrhodopsin-2 (ChR2), a light-sensitive ion channel of the green alga Chlamydomonas reinhardtii, to the auxiliary β1 subunit of voltage-gated Na+ channels. The resulting fusion construct, β1-ChR2, retained the ability to modulate Na+ channel kinetics and generate photosensitive inward currents. Stimulation of Xenopus oocytes coexpressing the skeletal muscle Na+ channel Nav1.4 and β1-ChR2 with 25-ms lasting blue-light pulses resulted in rapid alterations of the membrane potential strongly resembling typical action potentials of excitable cells. Blocking Nav1.4 with tetrodotoxin prevented the fast upstroke and the reversal of the membrane potential. Coexpression of the voltage-gated K+ channel Kv2.1 facilitated action potential repolarization considerably. Light-induced action potentials were also obtained by coexpressing β1-ChR2 with either the neuronal Na+ channel Nav1.2 or the cardiac-specific isoform Nav1.5. Potential applications of this novel optogenetic tool are discussed.

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