850 research outputs found
Electron probe microanalysis of calcium release and magnesium uptake by endoplasmic reticulum in bee photoreceptors.
Composition of vacuoles and sarcoplasmic reticulum in fatigued muscle: electron probe analysis.
Phosphorylation of telokin by cyclic nucleotide kinases and the identification of in vivo phosphorylation sites in smooth muscle
AbstractThe Ca2+-independent acceleration of dephosphorylation of the regulatory light chain of smooth muscle myosin and relaxation of smooth muscle by telokin are enhanced by cyclic nucleotide-activated protein kinase(s) [Wu et al. (1998) J. Biol. Chem. 273, 11362ā11369]. The purpose of this study was to determine the in vivo site(s) and in vitro rates of telokin phosphorylation and to evaluate the possible effects of sequential phosphorylation by different kinases. The in vivo site(s) of phosphorylation of telokin were determined in rabbit smooth muscles of longitudinal ileum and portal vein. Following stimulation of ileum with forskolin (20 Ī¼M) the serine at position 13 was the only amino acid to exhibit increased phosphorylation. Rabbit portal vein telokin was phosphorylated on both Ser-13 and -19 as a result of forskolin and GTPĪ³S stimulation in vivo. Point mutation of Ser-13 (to Ala or Asp) abolished in vitro phosphorylation by cyclic nucleotide-dependent protein kinases
Electron probe analysis of vascular smooth muscle. Composition of mitochondria, nuclei, and cytoplasm.
Kinetics of contraction initiated by flash photolysis of caged adenosine triphosphate in tonic and phasic smooth muscles.
Phasic contractions of isolated human myometrium are associated with Rho-kinase (ROCK)-dependent phosphorylation of myosin phosphatase-targeting subunit (MYPT1)
Force generation in smooth muscle is driven by phosphorylation of myosin light chains (MYL), which is regulated by the equilibrium between the activities of myosin light chain kinase (MYLK) and myosin phosphatase (MYLP). MYLK is activated by Ca2+-calmodulin whereas MYLP is inhibited by phosphorylation of its myosin-binding subunit (MYPT1) by Ca2+-independent mechanisms, leading to generation of increased MYL phosphorylation and force for a given intracellular Ca2+ concentration, a phenomenon known as ācalcium-sensitizationā. The regulation of MYPT1 phosphorylation in human myometrium, which shows increasing phasic contractility at the onset of labour, has yet to be fully investigated. Here, we explore phosphorylation of MYPT1 at Thr696 and Thr853, alongside phosphorylation of MYL, in fresh human myometrial tissue and cultured myometrial cells. We report that pMYPT1 (Thr853) levels are dependent on the activity of Rho-associated kinase (ROCK), determined using the ROCK inhibitor g-H-1152 and siRNA-mediated knockdown of ROCK1/2, and are highly correlated to ppMYL (Thr18/Ser19) levels. Pharmacological inhibition of ROCK was associated with a decrease in oxytocin (OXT)-stimulated contractility of myometrial strips in vitro. Moreover, we have measured pMYPT1 and pMYL levels between and during spontaneous and OXT-stimulated phasic contractions by rapidly freezing contracting muscle, and demonstrate for the first time functional coupling between increases in pMYPT1 (Thr853), ppMYL (Thr18/Ser19) and phasic contractility that is ROCK-dependent. The combined approach of measuring contractility and phosphorylation has demonstrated that the phosphorylation of MYPT1 (Thr853) changes dynamically with each contraction and has elucidated a defined role for ROCK in regulating myometrial contractility through MYLP, providing new insights into uterine physiology which will stimulate further research into treatments for preterm labour
Modulation of voltage-dependent Ca channel current by arachidonic acid and other long-chain fatty acids in rabbit intestinal smooth muscle.
Protein phosphatase composition in the smooth muscle of guinea-pig ileum studied with okadaic acid and inhibitor 2
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