SMB myosin heavy chain knockout enhances tonic contraction and reduces the rate of force generation in ileum and stomach antrum

Author:

Huang Qian1,Babu Gopal J.2,Periasamy Muthu3,Eddinger Thomas J.1

Affiliation:

1. Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin;

2. Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersery Medical School, Newark, New Jersey; and

3. Department of Physiology and Cell Biology, College of Medicine and Public Health, Ohio State University, Columbus, Ohio

Abstract

The role of SMA and SMB smooth muscle myosin heavy chain (MHC) isoforms in tonic and phasic contractions was studied in phasic (longitudinal ileum and stomach circular antrum) and tonic (stomach circular fundus) smooth muscle tissues of SMB knockout mice. Knocking out the SMB MHC gene eliminated SMB MHC protein expression and resulted in upregulation of the SMA MHC protein without altering the total MHC protein level. Switching from SMB to SMA MHC protein expression decreased the rate of the force transient and increased the sustained tonic force in SMB(−/−)ileum and antrum with high potassium (KPSS) but not with carbachol (CCh) stimulation. The increased tonic contraction under the depolarized condition was not through changes in second messenger signaling pathways (PKC/CPI-17 or Rho/ROCK signaling pathway) or LC20phosphorylation. Biochemical analyses showed that the expression of contractile regulatory proteins (MLCK, MLCP, PKCδ, and CPI-17) did not change significantly in tissues tested except for PKCα protein expression being significantly decreased in the SMB(−/−)antrum. However, specifically activating PKCα with phorbol dibutyrate (PDBu) was not significantly different in knockout and wild-type tissues, with total force being a fraction of the force generation with KPSS or CCh stimulation in SMB(−/−)ileum and antrum. Taken together, these data show removing the SMB MHC protein expression with a compensatory increase in the SMA MHC protein results in enhanced sustained KPSS-induced tonic contraction with a reduced rate of force generation in these phasic tissues.

Publisher

American Physiological Society

Subject

Cell Biology,Physiology

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