Abstract
The stomach serves as food reservoir, mixing organ and absorption area for certain substances, while continually varying its position and size. Large dimensional changes during ingestion and gastric emptying of the stomach are associated with large changes in smooth muscle length. These length changes might induce history-effects, namely force depression (FD) following active muscle shortening and force enhancement (FE) following active muscle stretch. Both effects have impact on the force generating capacity of the stomach, and thus functional relevance. However, less is known about history-effects and active smooth muscle properties of stomach smooth muscle. Thus, the aim of this study was to investigate biomechanical muscle properties as force-length and force-velocity relations (FVR) of porcine stomach smooth muscle strips, extended by the analysis of history-effects on smooth muscle force. Therefore, in total n = 54 tissue strips were dissected in longitudinal direction from the ventral fundus of porcine stomachs. Different isometric, isotonic, and isokinetic contraction protocols were performed during electrical muscle stimulation. Cross-sectional areas (CSA) of smooth muscles were determined from cryo-histological sections stained with Picrosirius Red. Results revealed that maximum smooth muscle tension was 10.4 ± 2.6 N/cm2. Maximum shortening velocity (Vmax) and curvature factor (curv) of the FVR were 0.04 ± 0.01 [optimum muscle length/s] and 0.36 ± 0.15, respectively. The findings of the present study demonstrated significant (P < 0.05) FD [up to 32% maximum muscle force (Fim)] and FE (up to 16% Fim) of gastric muscle tissue, respectively. The FE- and FD-values increased with increasing ramp amplitude. This outstanding muscle behavior is not accounted for in existing models so far and strongly supports the idea of a holistic reflection of distinct stomach structure and function. For the first time this study provides a comprehensive set of stomach smooth muscle parameters including classic biomechanical muscle properties and history-dependent effects, offering the possibility for the development and validation of computational stomach models. Furthermore, this data set facilitates novel insights in gastric motility and contraction behavior based on the re-evaluation of existing contractile mechanisms. That will likely help to understand physiological functions or dysfunctions in terms of gastric accommodation and emptying.
Highlights
Smooth musculature is located in the walls of various hollow organs, like the urinary bladder, the intestine, and the stomach; transporting several substances by muscle contraction
A comprehensive data set consisting of histological as well as specific biomechanical muscle properties
This study represents the first in-vitro approach that examined the influence of history-dependent effects induced by ramps with various lengths and velocities on stomach smooth muscle force
Summary
Smooth musculature is located in the walls of various hollow organs, like the urinary bladder, the intestine, and the stomach; transporting several substances (e.g., fluids, bolus, and nutrients) by muscle contraction. To better understand stomach motility and function, knowledge about the influence of muscle length, velocity, activation level, and history-dependent effects (Hill, 1938; Abbott and Aubert, 1952; Huxley and Hanson, 1954; Gordon et al, 1966; Ebashi and Endo, 1968; Rode et al, 2016) on smooth muscle force is required. While only a handful of studies have been observed forcevelocity relations (FVR) on guinea pigs (Moriya and Miyazaki, 1985) and toads (Warshaw, 1987), intensive research has been done on the relationship between muscle length and force production in a variety of vertebrate and invertebrate smooth muscles (Gordon and Siegman, 1971; Herlihy and Murphy, 1973). Almost nothing is known about the classic biomechanical properties as force-length and FVRs in the porcine stomach (Gunst, 1986; Minekus and van Mastrigt, 2001)
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