HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 288/3/R607    most recent 00612.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Dibb, K. M. Articles by Trafford, A. W. Search for Related Content PubMed PubMed Citation Articles by Dibb, K. M. Articles by Trafford, A. W.

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Photoperiod-dependent modulation of cardiac excitation contraction coupling in the Siberian hamster

¹Unit of Cardiac Physiology and ²School of Biological Sciences, The University of Manchester, Manchester, United Kingdom

Submitted 8 September 2004 ; accepted in final form 1 November 2004

In mammals, changes in photoperiod regulate a diverse array of physiological and behavioral processes, an example of which in the Siberian hamster (Phodopus sungorus) is the expression of bouts of daily torpor following prolonged exposure to a short photoperiod. During torpor, body temperature drops dramatically; however, unlike in nonhibernating or nontorpid species, the myocardium retains the ability to contract and is resistant to the development of arrhythmias. In the present study, we sought to determine whether exposure to a short photoperiod results in alterations to cardiac excitation-contraction coupling, thus potentially enabling the heart to survive periods of low temperature during torpor. Experiments were performed on single ventricular myocytes freshly isolated from the hearts of Siberian hamsters that had been exposed to either 12 wk of short-day lengths (SD) or 12 wk of long-day lengths (LD). In SD-acclimated animals, the amplitude of the systolic Ca²⁺ transient was increased (e.g., from 142 ± 17 nmol/l in LD to 229 ± 31 nmol/l in SD at 4 Hz; P < 0.001). The increased Ca²⁺ transient amplitude in the SD-acclimated animals was not associated with any change in the shape or duration of the action potential. However, sarcoplasmic reticulum Ca²⁺ content measured after current-clamp stimulation was increased in the SD-acclimated animals (at 4 Hz, 110 ± 5 vs. 141 ± 15 µmol/l, P < 0.05). We propose that short photoperiods reprogram the function of the cardiac sarcoplasmic reticulum, resulting in an increased Ca²⁺ content, and that this may be a necessary precursor for maintenance of cardiac function during winter torpor.

calcium; sarcoplasmic reticulum; torpor; action potential

This article has been cited by other articles:

				S. Miyazawa, Y. Shimizu, T. Shiina, H. Hirayama, H. Morita, and T. Takewaki Central A1-receptor activation associated with onset of torpor protects the heart against low temperature in the Syrian hamster Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2008; 295(3): R991 - R996. [Abstract] [Full Text] [PDF]

				T. Ruf and W. Arnold Effects of polyunsaturated fatty acids on hibernation and torpor: a review and hypothesis Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2008; 294(3): R1044 - R1052. [Abstract] [Full Text] [PDF]

				A. Mertens, O. Stiedl, S. Steinlechner, and M. Meyer Cardiac dynamics during daily torpor in the Djungarian hamster (Phodopus sungorus) Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2008; 294(2): R639 - R650. [Abstract] [Full Text] [PDF]

				F. I. J. Crawford, C. L. Hodgkinson, E. Ivanova, L. B. Logunova, G. J. Evans, S. Steinlechner, and A. S. I. Loudon Influence of torpor on cardiac expression of genes involved in the circadian clock and protein turnover in the Siberian hamster (Phodopus sungorus) Physiol Genomics, November 14, 2007; 31(3): 521 - 530. [Abstract] [Full Text] [PDF]