PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 9728491

Relationships between transmembrane action potential changes and simultaneous changes in electrocardiograms of rats after a one-month aortic pressure overload.

Y Lessard·L Vernhet·A Mainguy
View original source ↗Export metadata ↓

Abstract

An attempt was made to determine the relationship between the characteristics of electrical activity of the hypertrophied myocardium of rats at the cellular level and at the level of the whole heart after a one-month left ventricular pressure overload. Such an animal model has already been demonstrated to be highly resistant to epinephrine-induced arrhythmias. Since severe ventricular arrhythmias often occur in patients with cardiac hypertrophy, ventricular vulnerability might depend on some electrophysiological characteristics of the heart related to the stage of hypertrophy. Using the "floating" microelectrode technique, the computed characteristics of cardiac transmembrane action potentials (AP) of the left and right epicardium cells were compared in situ to computed characteristics of the electrocardiograms in anaesthetized control rats (group C) and in rats with left ventricular hypertrophy (group H) induced by a one-month suprarenal constriction of the abdominal aorta. The aortic pressure overload caused a significant (p<0.001) and marked increase in AP duration of left ventricular cells: APD 30 and APD 80 were 29+/-3 ms and 89+/-6 ms, respectively, in group H and 14+/-1 ms and 53+/-2 ms in group C. The same modifications were observed in right ventricular cells when right hypertrophy was present. Simultaneous electrocardiograms exhibited a significant (p<0.01) prolongation of P-R, Q-S and T duration and T wave flattening in group H (63+/-2 ms, 32+/-3 ms, 109+/-5 ms and 0.25+/-0.03 mV as compared with 53+/-1 ms, 20+/-1 ms, 88+/-2 ms and 0.40+/-0.04 mV in group C). After a one-month aortic overload in rats, both left and right ventricles are hypertrophied and have the same electrophysiological characteristics: in this model, at this stage of hypertrophy, some factors favouring ventricular arrhythmias are missing. The corresponding flattening of the T wave in the ECG might be of clinical relevance.

Explore related subjects

Action PotentialsAnimalsAortaElectrocardiographyHypertrophy, Left VentricularMaleRatsRats, WistarTime FactorsJournal ArticleResearch Support, Non-U.S. Gov't

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Y Lessard, L Vernhet, A Mainguy. 1997. Relationships between transmembrane action potential changes and simultaneous changes in electrocardiograms of rats after a one-month aortic pressure overload.. https://pubmed.ncbi.nlm.nih.gov/9728491/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2000

Cutting of living hippocampal slices by a highly pressurised water jet (macromingotome).

Living brain slices are usually cut with razor blades, which compress a ca. 50-microm-thick layer of tissue. This results in cell debris and lesioned cells which, e.g. form diffusion barriers between the bath and living neurons underneath, thereby prolonging response times of neurons to drugs in the bath saline and impeding the experimental access to intact neurons. To avoid such drawbacks, a macromingotome was developed which cuts nervous tissue with water jets. Physiological saline under pressures of 100-1800 bar was ejected through nozzles of 35-100 microm to cut 300-500-microm-thick hippocampal slices. Systematic variations of pressure and nozzle diameter revealed best results at 400-600 bar and with nozzle diameters of 60-80 microm. Under these conditions, intact CA1- and CA3-neurons as well as granule cells were detected with infrared microscopy at less than 10 microm underneath the surface of the slice. Superficial neurons with intact fine structures were also seen when the slices were studied by light-microscopy. Intra- and extracellular recordings from superficial neurons showed normal membrane- and full action potentials and the development of stable epileptiform discharges in 0 Mg(2+)-saline. These results indicate that the macromingotome offers an alternative way of cutting slices which may facilitate electrophysiological/neuropharmacological or fluorometric studies on superficial neurons.

Action Potentials↗
PubMed2000

Quantification of optical signals with electrophysiological signals in neural activities of Di-4-ANEPPS stained rat hippocampal slices.

We have quantified the optical signals of synaptically induced neural activities in an in vitro brain slice preparation in terms of electrophysiological signals. The qualification was done using electrophysiologically well known neural activities in the CA1 area of rat hippocampal slices stained with externally applied fluorescent voltage-sensitive dye (VSD; Di-4-ANEPPS). Together with a newly designed CCD-based digital high-speed camera system and epi-fluorescent optics, our improvements were made on a protocol for staining using a newly designed chamber system. These improvements enabled us to make stable and reliable recordings of optical signals and electrophysiological measurements without affecting the physiological status and to make a quantitative comparison between them. The time course and amplitude of the optical signal showed fair agreement with intracellular and extracellular recordings, and was stable over 2 h. The optical signal followed synaptically induced long-term potentiation (LTP) as monitored by the electrophysiological signals. A regional difference in the amount of LTP was found in optical signals and was confirmed in the electrophysiological signals. These results demonstrate the capabilities of our improved method as an alternative but more potent tool to measure the neuronal activities of brain slice in addition to electrophysiological method.

Action Potentials↗
PubMed2000

CRH-induced electrical activity and calcium signalling in pituitary corticotrophs.

Pituitary corticotroph cells generate repetitive action potentials and associated Ca2+ transients in response to the agonist corticotropin releasing hormone (CRH). There is indirect evidence suggesting that the agonist, by way of complex intracellular mechanisms, modulates the voltage sensitivity of the L-type Ca2+ channels embedded in the plasma membrane. We have previously constructed a Hodgkin-Huxley-type model of this process, which indicated that an increase in the L-type Ca2+ current is sufficient to generate repetitive action potentials (LeBeau et al. (1997). Biophys. J.73, 1263-1275). CRH is also believed to inhibit an inwardly rectifying K+ current. In this paper, we have found that a CRH-induced inhibition of the inwardly rectifying K+ current increases the model action potential firing frequency, [Ca2+]i transients and membrane excitability. This dual modulatory action of CRH on inward rectifier and voltage-gated Ca2+ channels better describes the observed CRH-induced effects. This structural alteration to the model along with parameter changes bring the model firing frequency in line with experimental data. We also show that the model exhibits experimentally observed bursting behaviour, where the depolarization spike is followed by small oscillations in the membrane potential.

Action Potentials↗