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Using a seasonal mammal exhibiting low temperature torpor to understand the physiology of cardiac myoctes and resistance arrhythmias

Reference	BB/C515139/1
Principal Investigator / Supervisor	Professor Andrew Trafford
Co-Investigators / Co-Supervisors	Professor Andrew Loudon, Professor Holly Shiels
Institution	The University of Manchester
Department	Medical and Human Sciences
Funding type	Research
Value (£)	311,578
Status	Completed
Type	Research Grant
Start date	01/10/2005
End date	30/09/2008
Duration	36 months

Abstract

This proposal will investigate a fascinating aspect of biology with important physiological and clinical ramifications; namely how the myocardium of animals that undergo hibernation or low-temperature torpor adapts to retain function during these periods and becomes resistant to the development of cardiac arrhythmias. Both of these observations, the retention of contractility and resistance to cardiac arrhythmias, clearly represent adaptive processes occurring in response to changes in day-length as they only occur in animals that are either actively hibernating exhibiting torpor or about to enter this state following several weeks of shortening daylight hours. Animals that do not normally hibernate ie. man, or those that show seasonal hibernation torpor but experiencing long daylight hours neither retain cardiac function nor show resistance to the development of cardiac arrhythmias when cardiac temperature is reduced. The main experimental objectives are; i) to determine the mechanisms that underlie the increased systolic calcium transient observed in the animal about to enter hibernation torpor (based on our preliminary data) and ii) define how the function of the sarcoplasmic reticulum is altered in response to photoperiodic change and the output of the seasonal timer of the brain. To address these experimental objectives we will employ an array of methodological approaches that will provide, for the first time in this field, an integrative assessment of cardiac function and remodelling in preparation for hibernation torpor. The new data that will be derived will encompass evaluation of gene and protein expression through to measurements of cellular calcium handling and quantitative assessment of sarcoplasmic reticulum function and calcium content. We will also dissect the effect that photoperiod and seasonal influences have on cardiac function by utilising the occurrence in our experimental animal, the Siberian hamster, of a natural refractoriness to prolonged exposure to short day-lengths and reversion to summer physiology. The main methods that will be adopted to achieve these objectives are as follows: 1. Gene Expression. We have a list of candidate genes that encode for proteins that we either know from our preliminary data, or suspect from their established roles in cardiac excitation contraction coupling, are likely to be differentially regulated in the adaptive responses of the myocardium to photic entrainment and seasonality. We will assess these transcripts using quantitative real-time reverse transcription polymerase chain reaction (TaqMan Q-PCR). This method is preferred as it offers high sensitivity compared to array based systems and we already appreciate that small changes in the amount of transcribed products have profound effects on cardiac excitation contraction coupling. 2. Protein Expression and Function. Here we will utilise standard Western blotting and tritiated binding assays to assess the levels of our identified candidate proteins. Co-immunoprecipitation experiments will determine the interaction between specific proteins known to have profound effects on cardiac excitation contraction coupling. Back phosphorylation assays will be used to determine how the response of the myocardium to adrenergic stimulation is altered in the hibernators heart. Finally, we will also use radio-ligand binding assays to assess the calcium sensitivity and temperature dependence of the calcium release channel of the sarcoplasmic reticulum. 3. Cellular Calcium Homeostasis and Physiology. In these in vitro experiments we will measure the intracellular concentrations of calcium and sodium in single cardiac myocytes. We will dissect the roles played by the surface membrane and the intracellular calcium store, the sarcoplasmic reticulum, in the genesis of the systolic calcium transient and how they respectively determine the properties of relaxation and response to adrenergic stimulation and initiation of arrhythmias.

Summary

unavailable

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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