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Title: Cytoplasmic free calcium, myosin light chain phosphorylation, and force in phasic and tonic smooth muscle
Authors: Himpens, Bernard ×
Matthijs, Gert
Somlyo, A V
Butler, T M
Somlyo, A P #
Issue Date: Mar-1989
Series Title: The Journal of general physiology. vol:92 issue:6 pages:713-29
Abstract: The time course of [Ca2+]i, tension, and myosin light chain phosphorylation were determined during prolonged depolarization with high K+ in intact tonic (rabbit pulmonary artery) and phasic (longitudinal layer of guinea pig ileum) smooth muscles. [Ca2+]i was monitored with the 340 nm/380 nm signal ratio of the fluorescent indicator fura-2. The fluorescence ratio had a similar time course in both muscle types during depolarization with 109 mM [K+]o; after a transient peak, there was a decline to 70% of its peak value in tonic smooth muscle, and to 60% in phasic smooth muscle. Tension, however, continued to increase in the pulmonary artery, while in the ileum it declined in parallel with the [Ca2+]i. On changing [K+]o from 109 to 20 mM, tension and [Ca2+]i either remained unchanged or declined in parallel in the pulmonary artery. Phosphorylation of the 20-kD myosin light chain, measured during stimulation of muscle strips with 109 mM [K+]o in another set of experiments, increased from 3% to a peak of 50% in the intact pulmonary artery, and then declined to a steady state value of 23%. In the intact ileum, a very rapid, early transient phosphorylation (up to 50%) at 2-3 s was seen. This transient declined by 30 s to a value that was close to the resting level (7%), while tension remained at 55% of its peak force. A quick release during maintained stimulation induced no detectable change in the [Ca2+]i in either type of smooth muscle. We discuss the possibility that the slowly rising tonic tension in pulmonary artery could be due to cooperativity between phosphorylated and nonphosphorylated crossbridges.
URI: 
ISSN: 0022-1295
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Physiology Section (-)
Clinical Genetics Section (-)
Laboratory of Molecular and Cellular Signaling
Department of Human Genetics - miscellaneous
× corresponding author
# (joint) last author

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