TY - JOUR
T1 - Determinants of the contractile properties in the embryonic chicken gizzard and aorta
AU - Ogut, Ozgur
AU - Brozovich, Frank V.
PY - 2000
Y1 - 2000
N2 - Smooth muscle is generally grouped into two classes of differing contractile properties. Tonic smooth muscles show slow rates of force activation and relaxation and slow speeds of shortening (V(max)) but force maintenance, whereas phasic smooth muscles show poor force maintenance but have fast V(max) and rapid rates of force activation and relaxation. We characterized the development of gizzard and aortic smooth muscle in embryonic chicks to identify the cellular determinants that define phasic (gizzard) and tonic (aortic) contractile properties. Early during development, tonic contractile properties are the default for both tissues. The gizzard develops phasic contractile properties between embryonic days (ED) 12 and 20, characterized primarily by rapid rates of force activation and relaxation compared with the aorta. The rapid rate of force activation correlates with expression of the acidic isoform of the 17-kDa essential myosin light chain (MLC(17a)). Previous data from in vitro motility assays (Rover AS, Frezon Y, and Trybus KM. J Muscle Res Cell Motil 18: 103-110, 1997) have postulated that myosin heavy chain (MHC) isoform expression is a determinant for V(max) in intact tissues. In the current study, differences in V(max) did not correlate with previously published differences in MHC or MLC(17a) isoforms. Rather, V(max) was increased with thiophosphorylation of the 20-kDa regulatory myosin light chain (MLC20) in the gizzard, suggesting that a significant internal load exists. Furthermore, V(max) in the gizzard increased during postnatal development without changes in MHC or MLC17 isoforms. Although the rate of MLC20 phosphorylation was similar at ED 20, the rate of MLC20 dephosphorylation was significantly higher in the gizzard versus the aorta, correlating with expression of the M130 isoform of the myosin binding subunit in the myosin light chain phosphatase (MLCP) holoenzyme. These results indicate that unique MLCP and MLC17 isoform expression marks the phasic contractile phenotype.
AB - Smooth muscle is generally grouped into two classes of differing contractile properties. Tonic smooth muscles show slow rates of force activation and relaxation and slow speeds of shortening (V(max)) but force maintenance, whereas phasic smooth muscles show poor force maintenance but have fast V(max) and rapid rates of force activation and relaxation. We characterized the development of gizzard and aortic smooth muscle in embryonic chicks to identify the cellular determinants that define phasic (gizzard) and tonic (aortic) contractile properties. Early during development, tonic contractile properties are the default for both tissues. The gizzard develops phasic contractile properties between embryonic days (ED) 12 and 20, characterized primarily by rapid rates of force activation and relaxation compared with the aorta. The rapid rate of force activation correlates with expression of the acidic isoform of the 17-kDa essential myosin light chain (MLC(17a)). Previous data from in vitro motility assays (Rover AS, Frezon Y, and Trybus KM. J Muscle Res Cell Motil 18: 103-110, 1997) have postulated that myosin heavy chain (MHC) isoform expression is a determinant for V(max) in intact tissues. In the current study, differences in V(max) did not correlate with previously published differences in MHC or MLC(17a) isoforms. Rather, V(max) was increased with thiophosphorylation of the 20-kDa regulatory myosin light chain (MLC20) in the gizzard, suggesting that a significant internal load exists. Furthermore, V(max) in the gizzard increased during postnatal development without changes in MHC or MLC17 isoforms. Although the rate of MLC20 phosphorylation was similar at ED 20, the rate of MLC20 dephosphorylation was significantly higher in the gizzard versus the aorta, correlating with expression of the M130 isoform of the myosin binding subunit in the myosin light chain phosphatase (MLCP) holoenzyme. These results indicate that unique MLCP and MLC17 isoform expression marks the phasic contractile phenotype.
KW - 17-kilodalton myosin light chain
KW - Development
KW - Force
KW - Phasic contractile properties
KW - Tonic smooth muscle
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U2 - 10.1152/ajpcell.2000.279.6.c1722
DO - 10.1152/ajpcell.2000.279.6.c1722
M3 - Article
C2 - 11078686
AN - SCOPUS:0033635907
SN - 0363-6143
VL - 279
SP - C1722-C1732
JO - American Journal of Physiology - Cell Physiology
JF - American Journal of Physiology - Cell Physiology
IS - 6 48-6
ER -