Nonmuscle Myosin motor of smooth muscle.
Nonmuscle myosin can generate force and shortening in smooth muscle, as revealed by studies of the urinary bladder from mice lacking smooth muscle myosin heavy chain (SM-MHC) but expressing the nonmuscle myosin heavy chains A and B (NM-MHC A and B; Morano, I., G.X. Chai, L.G. Baltas, V. Lamounier-Zepter, G. Lutsch, M. Kott, H. Haase, and M. Bader. 2000. Nat. Cell Biol. 2:371-375). Intracellular calcium was measured in urinary bladders from SM-MHC-deficient and SM-MHC-expressing mice in relaxed and contracted states. Similar intracellular [Ca2+] transients were observed in the two types of preparations, although the contraction of SM-MHC-deficient bladders was slow and lacked an initial peak in force. The difference in contraction kinetics thus do not reflect differences in calcium handling. Thick filaments were identified with electron microscopy in smooth muscle cells of SM-MHC-deficient bladders, showing that NM-MHC can form filaments in smooth muscle cells. Maximal shortening velocity of maximally activated, skinned smooth muscle preparations from SM-MHC-deficient mice was significantly lower and more sensitive to increased MgADP compared with velocity of SM-MHC-expressing preparations. Active force was significantly lower and less inhibited by increased inorganic phosphate. In conclusion, large differences in nucleotide and phosphate binding exist between smooth and nonmuscle myosins. High ADP binding and low phosphate dependence of nonmuscle myosin would influence both velocity of actin translocation and force generation to promote slow motility and economical force maintenance of the cell.
Löfgren
Mia
M
Department of Physiological Sciences, Medical Faculty, Lund University, SE-221 84 Lund, Sweden.
Ekblad
Eva
E
Morano
Ingo
I
Arner
Anders
A
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D007537:Isometric Contraction / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D020409:Molecular Motor Proteins / Q000172:deficiency / Q000502:physiology* / Q000648:ultrastructure*; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure*; D018995:Myosin Heavy Chains / Q000172:deficiency / Q000502:physiology*; D024501:Nonmuscle Myosin Type IIB; D010710:Phosphates / Q000378:metabolism; D024745:Smooth Muscle Myosins / Q000172:deficiency / Q000502:physiology*; D001743:Urinary Bladder / Q000166:cytology / Q000502:physiology
D020409:Molecular Motor Proteins; D010710:Phosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D024501:Nonmuscle Myosin Type IIB; D024745:Smooth Muscle Myosins; C103815:nonmuscle myosin type IIB heavy chain; D018995:Myosin Heavy Chains; D002118:Calcium