Publications by authors named "Diarmid Hall"

2 Publications

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Indirect evidence that anoxia exposure and cold acclimation alter transarcolemmal Ca flux in the cardiac pacemaker, right atrium and ventricle of the red-eared slider turtle (Trachemys scripta).

Comp Biochem Physiol A Mol Integr Physiol 2021 Nov 29;261:111043. Epub 2021 Jul 29.

Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, United States of America.

We indirectly assessed if altered transarcolemmal Ca flux accompanies the decreased cardiac activity displayed by Trachemys scripta with anoxia exposure and cold acclimation. Turtles were first acclimated to 21 °C or 5 °C and held under normoxic (21N; 5N) or anoxic conditions (21A; 5A). We then compared the response of intrinsic heart rate (f) and maximal developed force of spontaneously contracting right atria (F), and maximal developed force of isometrically-contracting ventricular strips (F), to Ni (0.1-10 mM), which respectively blocks T-type Ca channels, L-type Ca channels and the Na-Ca-exchanger at the low, intermediate and high concentrations employed. Dose-response curves were established in simulated in vivo normoxic (Sim Norm) or simulated in vivo anoxic extracellular conditions (Sim Anx; 21A and 5A preparations). Ni decreased intrinsic f, F and F of 21N tissues in a concentration-dependent manner, but the responses were blunted in 21A tissues in Sim Norm. Similarly, dose-response curves for F and F of 5N tissues were right-shifted, whereas anoxia exposure at 5 °C did not further alter the responses. The influence of Sim Anx was acclimation temperature-, cardiac chamber- and contractile parameter-dependent. Combined, the findings suggest that: (1) reduced transarcolemmal Ca flux in the cardiac pacemaker is a potential mechanism underlying the slowed intrinsic f of anoxic turtles at 21 °C, but not 5 °C, (2) a downregulation of transarcolemmal Ca flux may aid cardiac anoxia survival at 21 °C and prime the turtle myocardium for winter anoxia and (3) confirm that altered extracellular conditions with anoxia exposure can modify turtle cardiac transarcolemmal Ca flux.
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November 2021

Cardiophysiological responses of the air-breathing Alaska blackfish to cold acclimation and chronic hypoxic submergence at 5°C.

J Exp Biol 2020 11 16;223(Pt 22). Epub 2020 Nov 16.

Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK 99508, USA.

The Alaska blackfish () remains active at cold temperatures when experiencing aquatic hypoxia without air access. To discern the cardiophysiological adjustments that permit this behaviour, we quantified the effect of acclimation from 15°C to 5°C in normoxia (15N and 5N fish), as well as chronic hypoxic submergence (6-8 weeks; ∼6.3-8.4 kPa; no air access) at 5°C (5H fish), on and spontaneous heart rate ( ), electrocardiogram, ventricular action potential (AP) shape and duration (APD), the background inward rectifier ( ) and rapid delayed rectifier ( ) K currents and ventricular gene expression of proteins involved in excitation-contraction coupling. was ∼50% slower in 5N than in 15N fish, but 5H fish did not display hypoxic bradycardia. Atypically, cold acclimation in normoxia did not induce shortening of APD or alter resting membrane potential. Rather, QT interval and APD were ∼2.6-fold longer in 5N than in 15N fish because outward and were not upregulated in 5N fish. By contrast, chronic hypoxic submergence elicited a shortening of QT interval and APD, driven by an upregulation of The altered electrophysiology of 5H fish was accompanied by increased gene expression of (3.5-fold; K11.2 of ), (7.4-fold; K2.2 of ) and (2.9-fold; K2.4 of ). 5H fish also exhibited a unique gene expression pattern that suggests modification of ventricular Ca cycling. Overall, the findings reveal that Alaska blackfish exposed to chronic hypoxic submergence prioritize the continuation of cardiac performance to support an active lifestyle over reducing cardiac ATP demand.
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November 2020