The Concentrations of Total Calcium in Fast-Twitch and Heart Muscles from Mice in an Agitated and Active State is Almost 2-Fold Greater than those from Resting Mice

Abstract

Based on the recent observation that the concentration of total Ca in whole muscle ([CaT]WM) from mice increases as the ratio of whole-mouse weight to muscle weight increases, we hypothesized the presence of one or more physiological mechanisms that increase Ca content in order to increase the specific force of the muscle (Lamboley et al., 2015; J. Gen. Physiol., 145(2):127-153). This finding was observed in both fast-twitch (EDL) and slow-twitch muscle (soleus). More recently, we noted that 6- to 8-months-old mice in cages recently (within 5-15 minutes) transferred from the animal-care facility to our laboratory appeared agitated, spending a significant amount of time climbing up the sides and ceiling of their cages. Because of the results and hypothesis above, it seemed of interest to determine whether [CaT]WM was different for muscle tissues obtained from mice in this “active/agitated” state compared to [CaT]WM values obtained from “rested” mice, mice from the same cages after several hours of acclimatization to the new locale. For EDL, soleus, and left-ventricular muscle samples from mice in the “active/agitated” state, the average values (S.E.M.; N) of [CaT]WM in units of mmoles of Ca/kg of muscle were, respectively 4.05 (0.29; 8), 2.42 (0.23; 7), and 2.67 (0.25; 10) and the corresponding average values with the “rested” mice were 2.25 (0.29, 8), 2.32 (0.77; 7), and 1.42 (0.31, 10). For the EDL and heart muscles only, the average values of [CaT]WM were significantly greater (p = 0.005 and 0.006, respectively) for the “active/agitated” vs. “rested” state, by factors of 1.80 and 1.88, respectively. The increases are likely due to adrenergic stimulation and/or increased use of the affected muscles.