Increasing intramuscular fluid volume increases passive tension in mammalian skeletal muscle

Experimental work in amphibian skeletal muscle and modeling studies have demonstrated that intramuscular fluid volume is an important determinant of the passive force that develops during lengthening. However, this effect has yet to be investigated in mammalian skeletal muscle. Therefore, we exposed isolated mouse soleus and extensor digitorum longus (EDL) muscles to a graded series of hypotonic solutions to promote fluid uptake while measuring passive force development, muscle mass, and 2D projected muscle area. Normalized to the tension measured at 1.2 L0 in isotonic Ringer’s solution, the relative passive forces in the soleus were 1.14, 1.31, 1.52, and 1.92 in 70%, 60%, 55%, and 50% relative tonicity, respectively. Comparable values for the EDL in relative tonicities of 70%, 60%, and 55% were 1.13, 1.78, and 2.10, respectively. In both muscles, increases in passive force were accompanied by increases in mass and projected area. We also investigated the effect of muscle tension on flu..., Animals Female CD-1 Mice (Mus musculus [16]) were acquired from Charles River Laboratories in Wilmington, MA and were 10 - 20 weeks of age when used. All animal use was approved by the Brown University Institutional Animal Care and Use Committee. Muscle dissection and in vitro setup for force measurements Muscles were isolated from both hindlimbs of each animal (soleus, N=6 animals; EDL, N=7 animals). For the EDL, only the head to the fifth toe was used. One muscle from each pair was used to acquire passive tension measurements, and the contralateral muscle was used as a control to obtain a measure of untreated muscle mass. Immediately following dissection, isolated muscles were placed into oxygenated mammalian Ringer’s solution [17]consisting of 144 mmol 1-1 NaCl, 6 mmol 1-1 KCl, 2 mmol 1-1 CaCl2, 1 mmol 1-1 MgSO4, 1 mmol 1-1 NaH2PO4 H2O, 10 mmol 1-1glucose, and 10 mmol 1-1 Hepes, and adjusted to a pH of 7.4 using 1 molar Tris base. Assuming complete ionization, this Ringer’s..., # Increasing intramuscular fluid volume increases passive tension in mammalian skeletal muscle Dataset DOI: [10.5061/dryad.d7wm37qdx](https://doi.org/10.5061/dryad.d7wm37qdx) ## Description of the data and file structure **File 1: Soleus and EDL Passive Force at 1.2L~0~** **(Force_at_1.2L0.csv)** **A.**      Here, you can find the relative passive force values at 1.2 L~0~ for soleus and EDL preps. All hypotonic passive force values are shown relative to their corresponding isotonic passive force values. Note that these values are uncorrected for the effects of repeated passive lengthening (shown later in **B** and **C**). **B.**      The next set of data contains passive force values at 1.2 L~0~ in our experiments to determine the effect of repeated lengthening on passive force. Note that these experiments were only conducted in isotonic solution, but that lengthening bouts were matched based on time to the lengthening event they correspond with in our hypotonic experiments (**A*..., ,