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Decreased shortening velocity and altered myosin isoforms in guinea‐pig hypertrophic intestinal smooth muscle
Author(s) -
Löfgren Mia,
Fagher Katarina,
Wede Oskar Karlsson,
Arner Anders
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.027060
Subject(s) - myosin , muscle hypertrophy , actin , biology , medicine , endocrinology , guinea pig , small intestine , gene isoform , isometric exercise , myosin light chain kinase , smooth muscle tissue , hypertrophic pyloric stenosis , anatomy , chemistry , biophysics , biochemistry , smooth muscle , gene
The aims of this study were to investigate whether hypertrophy of the small intestinal smooth muscle leads to alterations of myosin isoform composition and shortening velocity and whether possible changes correlate with a change in the sensitivity to ADP of shortening velocity in this tissue. A partial occlusion was introduced in the distal part of the ileum of guinea‐pigs. After 2 weeks, the part of the small intestine just proximal of the stenosis was hypertrophied (indicated by a significantly increased cross‐sectional area). The most proximal part of the small intestine was used as control, thus enabling comparisons between hypertrophic and normal tissue from the same animal. The outer longitudinal layer of the intestinal wall was gently peeled off and used for biochemistry, RT‐PCR and mechanical experiments. The desmin/actin ratio was significantly increased following hypertrophy, although myosin and actin expression were similar in control and hypertrophic tissue. In hypertrophic tissue, the myosin heavy chain mRNA with a 21 base pair insert decreased significantly. The composition of the mRNA encoding the myosin essential light chains changed towards more of the basic type (LC17b). No change in the expression of non‐muscle myosin heavy chains A and B was detected. The maximal shortening velocity ( V max ) of maximally activated skinned preparations was significantly lower in the hypertrophic tissue (≈50 % of control). The sensitivity of V max to ADP was increased in the hypertrophic smooth muscle tissue. We conclude that myosin expression is altered following intestinal hypertrophy and that these alterations affect reactions in the cross‐bridge interaction, leading to a slower and more economical contractile function.