12-1 The Diaphragm – Not only a Muscle for Respiration

The Diaphragm – Not only a Muscle for Respiration
Eli Carmeli, PhD, Einat Kodesh, PhD, Miri Maor, DDS

Abstract

Background: The diaphragm is actually two muscles, which are differentiated one from the other by structural, physiological and functional characteristics. The anterior (sternal) portion is a respiratory muscle while the posterior (crural) portion acts as a sphincter around the esophagus, preventing gastric reflux.

Aim: To investigate the effect of running on both portions of the diaphragm muscle

Methods: Four-month-old Sprague-Dawley rats (n=13) were divided into three groups. Group 1 (slow running) ran for 3 weeks at a rate of 18 m/min; Group 2 (fast running) ran for 3 weeks at the rate of 32 m/min; and Group 3 ran for 1 week and thereafter functioned as a control group. The running time for the first two groups was gradually increased; they started with 15 minutes of running, and each day 2 minutes were added so that 3 weeks later, after 15 days of actual training, the rats were running for 45 minutes. Immediately after their final run, the rats were sacrificed and both areas of the diaphragm were removed. Biochemical analysis at the protein level (using western blot) and at the level of messenger RNA, using reverse transcriptase-polymerase chain reaction (RT-PCR), was performed, and the level of activity of the copper-zinc superoxide dismutase enzyme (CuZn SOD1) was determined.

Results: In the fast running group, levels of CuZn SOD1 decreased significantly in the posterior diaphragm, while levels of the enzyme remained unchanged in the anterior diaphragm. Levels of protein and of the RNA messenger of matrix metalloproteinase type 2 increased after both fast and slow running, particularly in the posterior diaphragm.

Conclusion: The crural diaphragm muscle fibers, which contain significantly more type IIb fibers, were more strongly affected following fast running than sternal/costal diaphragm muscle fibers, which contain an equal distribution of slow twitch (type I) and fast twitch (type IIb) muscle fibers.