Morphological, histochemical, and myosin isoform analysis of the diaphragm of adult horses, Equus caballus.

The research is about the examination of the composition, structure, and functionality of the diaphragm in adult horses. The researchers believed that horses could present a conducive model for studying mammalian diaphragms.

Research Methodology

• The diaphragms of seven adult horses were prepared for various tests including histochemistry, immunocytochemistry, myosin heavy chain electrophoresis, and native myosin electrophoresis.
• Two more adult horses were dissected and stained with acetylcholinesterase to highlight motor endplates (the areas of muscles that are receptive to nerve impulses) and to show the morphology of the myofiber and central tendon.

Findings

• Every part of the adult horse diaphragm was predominantly composed of type I fibers, also observing some type IIa fibers. Type IIb fibers were absent in all the examined adult horse diaphragms.
• The myosin heavy chain electrophoresis results correlated with the histochemical results: they found two bands of myosin isoforms that moved at the same pace as rat type I and IIa myosin heavy chain isoforms. There were no isoforms found that coincided with the rat type IIb heavy chain isoforms.
• The native myosin isoform analysis found two forms that moved at the same pace as rat FM-4 and FM-3, and two more moving at the same pace as rat SM-1 and SM-2. Of interest, a third, slower myosin isoform was found in some samples, coursing at the same pace as the SM-3 of the equine biceps brachii muscle. This slow isoform was discovered to be exclusive to horse muscles in comparison with the other adult animals examined.

Implications of the Study

• The research team did not provide concrete interpretation on whether these multiple slow native myosin isoforms found in horse muscles give the animals a functional advantage over other creatures.
• However, they noted that the adult horse diaphragm is distinctly large, has a significant central tendon compared to other mammals, and is mainly composed of slow fiber types and myosin isoform structure which could suggest specialized function or adaptation.