Gastroenterology

Gastroenterology

Volume 121, Issue 5, November 2001, Pages 1209-1218
Gastroenterology

Basic Research
Altered cellular calcium regulatory systems in a rat model of cirrhotic cardiomyopathy,☆☆

https://doi.org/10.1053/gast.2001.28653Get rights and content

Abstract

Background & Aims: Decreased cardiac contractility has been observed in cirrhosis, but the cause remains unclear. Because cardiomyocyte contraction depends on Ca2+ influx entering via L-type Ca2+ channels (ICa,Ls) to activate Ca2+ release from the sarcoplasmic reticulum, we postulated that the Ca2+ transients may be abnormal in cirrhotic cardiomyocytes. We aimed to investigate the status of the cellular Ca2+-regulatory system in a rat model of cirrhotic cardiomyopathy. Methods: Cirrhosis was induced by bile duct ligation. The ICa,L protein expression was detected by Western blotting. Ca2+ currents were measured electrophysiologically. The intracellular Ca2+ system, which includes the ryanodine receptor 2 (RYR2), sarcoplasmic reticulum Ca2+-pump adenosine triphosphatase (SERCA2), and Ca2+-binding protein were quantitatively assayed by reverse-transcription polymerase chain reaction and Western blots and functionally by 3H-ryanodine binding and radiolabeled Ca2+ uptake. Results: ICa,L protein expression was reduced in cirrhotic rats compared with controls, and the peak inward Ca2+ current was significantly less. At all membrane potentials examined, ICa,Ls current densities from cirrhotic animals were consistently lower, and the response to maximal isoproterenol stimulation was also significantly lower. Protein expression and messenger RNA transcription for RYR2, SERCA2, and calsequestrin were quantitatively unchanged, and 3H-ryanodine binding characteristics and Ca2+ uptake were also unaltered. Conclusions: We conclude that the decreased cardiac contractility in cirrhotic cardiomyocytes is caused by dysfunction of the Ca2+-regulatory system. Plasma membrane ICa,Ls are quantitatively reduced and functionally depressed, whereas intracellular systems are intact.

GASTROENTEROLOGY 2001;121:1209-1218

Section snippets

Solutions, reagents, and enzymes

DNA synthase, RNA superscript synthase, and polymerase chain reaction buffer were purchased from Gibco BRL, Life Technologies Inc. (Gaithersburg, MD). Agarose was obtained from ICN Biomedicals Inc. (Aurora, OH), anti-RYR antibody was purchased in DSHB (University of Iowa, Iowa City, IA). The standard Tyrode solution contains 140 mmol/L NaCl, 5.4 mmol/L KCl, 1 mmol/L MgCl2, 1 mmol/L Na2HPO4, 5 mmol/L HEPES, and 10 mmol/L glucose; pH was adjusted to 7.4 with 1 mol/L NaOH and continuously gassed

Cardiomyocyte contractility

Isolated cardiomyocyte contractile studies showed that both baseline and isoproterenol-stimulated contractility were significantly decreased in BDL-treated rats compared with sham controls (Figure 1).

. Baseline and isoproterenol- and forskolin-stimulated isolated cardiomyocyte contractility in cirrhotic and control rats. Significantly different from corresponding baseline values: **P < 0.01.

Baseline values for fractional shortening were 8.0% ± 1.0% in control (n = 11) and 2.8% ± 0.4% in

Discussion

Cardiovascular anomalies associated with hepatic cirrhosis were first described almost half a century ago, with the initial descriptions of hyperdynamic circulation,25 followed in the late 1960s by reports of depressed ventricular contractile function in patients with alcoholic cirrhosis.2 These were believed to be manifestations of mild or latent alcoholic cardiomyopathy. Only in the past 15 years has it become clear that this ventricular dysfunction is associated with cirrhosis per se,

Acknowledgements

Drs. Ward and Liu contributed equally to this work.

References (39)

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Address requests for reprints to: Samuel S. Lee, M.D., 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada. e-mail: [email protected]; fax: (403) 270-0995.

☆☆

Supported by an operating research grant from the Canadian Institutes of Health Research. Dr. Liu was supported by a Canadian Association for the Study of Liver (CASL)—Amgen Research Fellowship award, and Dr. Lee was supported by an Alberta Heritage Foundation for Medical Research Senior Scholarship award.

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