title: Single rabbit stomach smooth muscle cell myosin heavy chain SMB expression and shortening velocity.
abstract: Isolated single smooth muscle cells (SMCs) from different regions of the rabbit stomach were used to determine a possible correlation between unloaded shortening velocity and smooth muscle (SM) myosin heavy chain (MHC) S1 head isoform composition (SMA, no head insert; SMB, with head insert). alpha-Toxin-permeabilized isolated single cells were maximally activated to measure unloaded shortening velocity and subsequently used in an RT-PCR reaction to determine the SMA/SMB content of the same cell. SM MHC SMA and SMB isoforms are uniquely distributed in the stomach with cells from the fundic region expressing little SMB (38.1 +/- 7.3% SMB; n = 16); cells from the antrum express primarily SMB (94.9 +/- 1.0% SMB; n = 16). Mean fundic cell unloaded shortening velocity was 0.014 +/- 0.002 cell lengths/s compared with 0.036 +/- 0.002 for the antrum cells. Unloaded shortening velocity in these cells was significantly correlated with their percent SMB expression (r2 = 0.58). Resting cell length does not correlate with the percent SMB expression (n = 32 cells). Previously published assays of purified or expressed SMA and SMB heavy meromyosin show a twofold difference in actin filament sliding speed in in vitro motility assays. Extrapolation of our data to 0-100% SMB would give a 10-fold range of shortening velocity, which is closer to the approximately 20-fold range reported from various SM tissues. This suggests that mechanisms in addition to the MHC S1 head isoforms regulate shortening velocity.
authors.affiliation: Department of Biology, Marquette University, Milwaukee, Wisconsin 5320l-1881, USA. thomas.eddinger@marquette.edu
authors.forename: T J
authors.initials: TJ
authors.lastname: Eddinger
authors.forename: D P
authors.initials: DP
authors.lastname: Meer
mesh_terms: D000818:Animals; D001324:Autoantigens / Q000378:metabolism*; D005753:Gastric Mucosa / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism*; D013270:Stomach / Q000166:cytology
chemical_list: D001324:Autoantigens; D020033:Protein Isoforms; D012333:RNA, Messenger; D017411:Ribonucleoproteins, Small Nuclear; D018995:Myosin Heavy Chains