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A Xenopus oocyte model system to study action potentials.

ABSTRACT: Action potentials (APs) are the functional units of fast electrical signaling in excitable cells. The upstroke and downstroke of an AP is generated by the competing and asynchronous action of Na⁺- and K⁺-selective voltage-gated conductances. Although a mixture of voltage-gated channels has been long recognized to contribute to the generation and temporal characteristics of the AP, understanding how each of these proteins function and are regulated during electrical signaling remains the subject of intense research. AP properties vary among different cellular types because of the expression diversity, subcellular location, and modulation of ion channels. These complexities, in addition to the functional coupling of these proteins by membrane potential, make it challenging to understand the roles of different channels in initiating and "temporally shaping" the AP. Here, to address this problem, we focus our efforts on finding conditions that allow reliable AP recordings from Xenopus laevis oocytes coexpressing Na⁺ and K⁺ channels. As a proof of principle, we show how the expression of a variety of K⁺ channel subtypes can modulate excitability in this minimal model system. This approach raises the prospect of studies on the modulation of APs by pharmacological or biological means with a controlled background of Na⁺ and K⁺ channel expression.

SUBMITTER: Corbin-Leftwich A

PROVIDER: S-EPMC6219683 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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A Xenopus oocyte model system to study action potentials.

Corbin-Leftwich Aaron A Small Hannah E HE Robinson Helen H HH Villalba-Galea Carlos A CA Boland Linda M LM

The Journal of general physiology 20180928 11

Action potentials (APs) are the functional units of fast electrical signaling in excitable cells. The upstroke and downstroke of an AP is generated by the competing and asynchronous action of Na+- and K+-selective voltage-gated conductances. Although a mixture of voltage-gated channels has been long recognized to contribute to the generation and temporal characteristics of the AP, understanding how each of these proteins function and are regulated during electrical signalin ...[more]

PMID: 30266757

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Project description:To investigate the effects of adenosine on endogenous Xenopus oocyte receptors, we analysed defolliculated oocytes injected with mRNAs for the G protein-activated inwardly rectifying K(+) (GIRK) channels. In oocytes injected with mRNAs for either GIRK1/GIRK2 or GIRK1/GIRK4 subunits, application of adenosine or ATP reversibly induced inward K(+) currents, although ATP was less potent than adenosine. The responses were attenuated by caffeine, a non-selective adenosine receptor antagonist. Furthermore, in uninjected oocytes from the same donor, adenosine produced no significant current. The endogenous receptor was activated by two selective A(1) adenosine receptor agonists, N(6)-cyclopentyladenosine (CPA) and N(6)-cyclohexyladenosine (CHA), and antagonized by a selective A(1) adenosine receptor antagonist, 1,3-dipropyl-8-cyclopenylxanthine (DPCPX) at moderate nanomolar concentrations, but insensitive to micromolar concentrations of selective A(2A) and A(3) adenosine receptor agonists, 2-[p-(2-carbonyl-ethyl)-phenylethylamino]-5'-N-ethylcarboxamidoadenosine (CGS21680) and N(6)-(3-iodobenzyl)-5'-(N-methylcarbamoyl)adenosine (IB-MECA), respectively. However, the pharmacological characteristics of the receptor were different from those of the cloned Xenopus A(1) adenosine receptor and previously proposed adenosine receptors. The adenosine-induced GIRK currents were abolished by injection of pertussis toxin and CPA inhibited forskolin-stimulated cyclic AMP accumulation. We conclude that an adenosine receptor on the Xenopus oocyte membrane can activate GIRK channels and inhibit adenylyl cyclase via G(i/o) proteins. Moreover, our results suggest the existence of an endogenous adenosine receptor with the unique pharmacological characteristics. As the receptor was activated by nanomolar concentrations of adenosine, which is a normal constituent of extracellular fluid, the receptor may be involved in some effects through the G(i/o) protein signalling pathways in ovarian physiology.

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A Xenopus oocyte model system to study action potentials.

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A <i>Xenopus</i> oocyte model system to study action potentials.

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