Smooth-muscle contraction without smooth-muscle myosin |
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Authors: | Morano I Chai G X Baltas L G Lamounier-Zepter V Lutsch G Kott M Haase H Bader M |
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Institution: | Max Delbrück Center for Molecular Medicine (MDC), Robert-R?ssle-Strabe 10, D-13092 Berlin, Germany. |
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Abstract: | Here we have used gene-targeting to eliminate expression of smooth-muscle myosin heavy chain. Elimination of this gene does not affect expression of non-muscle myosin heavy chain, and knockout individuals typically survive for three days. Prolonged activation, by KCl depolarisation, of intact bladder preparations from wild-type neonatal mice produces an initial transient state (phase 1) of high force generation and maximal shortening velocity, which is followed by a sustained state (phase 2) characterized by low force generation and maximal shortening velocity. Similar preparations from knockout neonatal mice do not undergo phase 1, but exhibit a normal phase 2. We propose that, in neonatal smooth muscle phase 1 is generated by recruitment of smooth-muscle myosin heavy chain, whereas phase 2 can be generated by activation of non-muscle myosin heavy chain. We conclude that phase 1 becomes indispensable for survival and normal growth soon after birth, particularly for functions such as homeostasis and circulation. |
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