Ca2+ uptake by cardiac sarcoplasmic reticulum at low temperature in rat and ground squirrel

Abstract

The Ca2+ uptake by isolated cardiac sarcoplasmic reticulum (SR) was compared between Richardson's ground squirrels and rats at 37, 25, 15, and 5 degrees C. The rate of SR Ca2+ uptake in ground squirrels was significantly higher than in rats over the temperature range. This marked species difference was observed over a Ca2+ concentration range from 0.1 to 10 microM. The Arrhenius plot for Ca2+ uptake was linear for ground squirrels between 37 and 5 degrees C but showed a depression from linearity for rats at 5 degrees C. This temperature sensitivity was also reflected in rat SR Ca2+-adenosinetriphosphatase activity. Analysis of [3H]ryanodine binding in SR suggests that more Ca2+ release channels are in an open state at low temperatures in rats than in ground squirrels. Together, these results suggest that species differences in the response of SR to low temperature may account for the rise in cytosolic free Ca2+ in cold-sensitive species and may be responsible, at least in part, for the inability of cold-sensitive hearts to function at low temperature.

Is cold acclimation of benefit to hibernating rodents?

“…Interestingly, no changes were noted in the preceding period, which we suggest may correspond to 'cold acclimation' of the present study. Taken together with our data, these observations indicate that the transition into torpor may increase the vulnerability to changes in core temperature (as exemplified by our data), but that during torpor, cardiac-specific changes to increase Ca 2+ transient amplitude may improve cardiovascular performance at lower core temperatures (Dibb et al, 2005;Liu et al, 1997).…”

“…In part, this may result from altered cardiac excitation-contraction coupling, manifested as increased Ca 2+ reuptake into the sarcoplasmic reticulum (Liu et al, 1997) and increased cardiac myofilament Ca 2+ sensitivity, at low temperatures (Liu et al, 1993). Indeed, Siberian hamsters showed increased Ca 2+ transient amplitude and increased Ca 2+ flux in cardiomyocytes following exposure to short photoperiod (Dibb et al, 2005), consistent with preserved contractile performance during seasonal hypothermia.…”

Digital transcriptome analysis indicates adaptive mechanisms in the heart of a hibernating mammal

“…This includes a significant increase in SERCA2a and a significant decrease in its membranebound negative regulator PLB during hibernation. These same two proteins have been recently found to be differentially regulated in the hearts of hibernating marmots (40), and their levels suggest enhanced cytoplasmic clearance of Ca 2ϩ during relaxation, possibly accounting for the uninterrupted rhythmic contractility in hibernators at temperatures that cause rat hearts to fail (18). This differential gene expression provides an explanation for the increased rate of Ca 2ϩ reuptake and larger calcium stores observed in the hibernating Spermophilus richardsonii sarcoplasmic reticulum (5).…”

In situcardiac performance of Pacific bluefin tuna hearts in response to acute temperature change

“…SR contributes to cardiac function by providing an intracellular calcium store, thereby reducing diffusion distances and accelerating rates of force development and relaxation (Bers, 2002). Increased SR contribution to E-C coupling is commonly implicated in myocardial cold tolerance in studies of cold-acclimation in fish (Keen et al, 1994;Aho and Vornanen, 1998) and hibernation in mammals (Liu et al, 1997). While the SR was long thought to play a minimal role in teleost hearts (Farrell and Jones, 1992), recent work has begun to clarify its importance in a variety of fish species.…”