Heart failure decreases passive tension generation of rat diaphragm fibers.
BACKGROUND
Diaphragm dysfunction is well-known to limit quality of life and prognosis of patients with heart failure (HF), but its underlying mechanisms are not well understood. In an animal model for HF we recently showed that impaired diaphragm contractility arises at the single fiber level and is associated with sarcomeric injuries. For optimal muscle function and sarcomeric stability passive elastic structures, like titin, are indispensable. The current study aimed to investigate if impaired passive elasticity contributes to diaphragm dysfunction in rats with heart failure.


METHODS
Skinned muscle fibers were isolated from the diaphragm and soleus of rats with chronic HF, induced by left coronary artery ligation and of sham-operated rats. Passive tension-length relationships were determined by applying segmental extension tests. Immunofluorescence was performed on muscle cryosections using antibodies (T12) against a titin epitope near the Z-line. Titin content was determined by SDS-agarose-gel electrophoresis. Titin's mobility on gel was studied to detect changes in titin size.


RESULTS
Passive tension generation upon stretch was significantly reduced (>35%) in HF diaphragm fibers compared to sham. Immunostaining intensities against titin were reduced in diaphragm cryosections of HF rats compared to sham. Soleus fibers from HF and sham rats did not display differences, neither in passive tension nor in immunostaining. No differences in titin's size were detected in HF and sham diaphragm. Titin content, however, was significantly reduced ( approximately 25%) in HF diaphragm.


CONCLUSIONS
We conclude that in the diaphragm of HF rats, passive elasticity is impaired, mainly resulting from titin loss.
van Hees
H W H
HW
Dept of Pulmonary Diseases, Radboud University Nijmegen Medical Centre, The Netherlands. h.vanhees@long.umcn.nl
Ottenheijm
C A C
CA
Granzier
H L
HL
Dekhuijzen
P N R
PN
Heunks
L M A
LM
D000818:Animals; D064211:Connectin; D003964:Diaphragm / Q000166:cytology / Q000378:metabolism / Q000503:physiopathology*; D004195:Disease Models, Animal; D004548:Elasticity; D004587:Electrophoresis, Agar Gel; D005455:Fluorescent Antibody Technique; D006333:Heart Failure / Q000503:physiopathology*; D008297:Male; D008970:Molecular Weight; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D009124:Muscle Proteins / Q000737:chemistry / Q000378:metabolism*; D009129:Muscle Tonus / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism / Q000503:physiopathology; D018995:Myosin Heavy Chains / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D064211:Connectin; D009124:Muscle Proteins; C577295:Ttn protein, rat; D018995:Myosin Heavy Chains