Calmodulin release

Walsh We have gone through several repetitive wash cycles and quantified the calmodulin release. It is barely detectable. The TFP is actually competing directly with MLCK for the same site on calmodulin, so I think it is simply a question of concentration. The TFP concentration is 0.4 mM. 

The VIA enzyme is sensitive to intracellular calcium stores and is inhibited by binding to calmodulin. Release of calmodulin upon depletion of calcium stores leads to activation of the enzyme (M.J. Wolf, 1997). The binding site for calmodulin on the enzyme has been identified as primarily residing within the 15-kDa C-terminus of the protein (C.M. Jenkins, 2001). It is proposed that the activation of VIA during depletion of intracellular calcium stores results in lysophosphatidylcholine production, which activates store-operated Ca + entry (T. Smani, 2003, 2004). 

Another mechanism in initiating the contraction is agonist-induced contraction. It results from the hydrolysis of membrane phosphatidylinositol and the formation of inositol triphosphate (IP3)- IP3 in turn triggers the release of intracellular calcium from the sarcoplasmic reticulum and the influx of more extracellular calcium. The third mechanism in triggering the smooth muscle contraction is the increase of calcium influx through the receptor-operated channels. The increased cytosolic calcium enhances the binding to the protein, calmodulin [73298-54-1]. 

The ETa receptor activates G proteins of the Gq/n and G12/i3 family. The ETB receptor stimulates G proteins of the G and Gq/11 family. In endothelial cells, activation of the ETB receptor stimulates the release of NO and prostacyclin (PGI2) via pertussis toxin-sensitive G proteins. In smooth muscle cells, the activation of ETA receptors leads to an increase of intracellular calcium via pertussis toxin-insensitive G proteins of the Gq/11 family and to an activation of Rho proteins most likely via G proteins of the Gi2/i3 family. Increase of intracellular calcium results in a calmodulin-dependent activation of the myosin light chain kinase (MLCK, Fig. 2). MLCK phosphorylates the 20 kDa myosin light chain (MLC-20), which then stimulates actin-myosin interaction of vascular smooth muscle cells resulting in vasoconstriction. Since activated Rho... 

Figure 1. Simplified schematic of receptor-mediated signal transduction in neutrophils. Binding of ligand to the receptor activates a guanine-nucleotide-binding protein (G protein), which then stimulates phospholipase C. Phosphatidylinositol 4,5-bis-phosphate is cleaved to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). DAG stimulates protein kinase C. IP3 causes the release of Ca from intracellular stores, which results in an increase in the cytosolic Ca concentration. This increase in Ca may stimulate protein kinase C, calmodulin-dependent protein kinases, and phospholipase A2. Protein phosphorylation events are thought to be important in stimulating degranulation and oxidant production. In addition, ionic fluxes occur across the plasma membrane. It is possible that phospholipase A2 and ionic channels may be governed by G protein interactions. ...

In addition to its effects on enzymes and ion transport, Ca /calmodulin regulates the activity of many structural elements in cells. These include the actin-myosin complex of smooth muscle, which is under (3-adrenergic control, and various microfilament-medi-ated processes in noncontractile cells, including cell motility, cell conformation changes, mitosis, granule release, and endocytosis. 

Calmodulin, a calcium binding protein, is involved in Ca2+-dependent regulation of several synaptic functions of the brain synthesis, uptake and release of neurotransmitters, protein phosphorylation and Ca+2 transport. It reacts with TET, TMT and TBT which then inactivates enzymes like Ca+2-ATPase and phosphodiesterase. In vitro studies indicated TBT was greater at inhibiting calmodulin activity than TET and TMT, whereas in vivo the order was TET > TMT > TBT. This may be due to the greater detoxification of TBT (66%) in the liver before moving to other organs30,31. 

Ca2+,calmodulin-dependent May transiently associate with synaptic vesicles to phosphorylate synapsins and rabphilin-3A. May regulate various protein kinases I and II steps in neurotransmitter release. 

The synthesis of 5-HT can increase markedly under conditions requiring more neurotransmitter. Plasticity is an important concept in neurobiology. In general, this refers to the ability of neuronal systems to conform to either short- or long-term demands placed upon their activity or function (see Plasticity in Ch. 53). One of the processes contributing to neuronal plasticity is the ability to increase the rate of neurotransmitter synthesis and release in response to increased neuronal activity. Serotonergic neurons have this capability the synthesis of 5-HT from tryptophan is increased in a frequency-dependent manner in response to electrical stimulation of serotonergic soma [7]. The increase in synthesis results from the enhanced conversion of tryptophan to 5-HTP and is dependent on extracellular calcium ion. It is likely that the increased 5-HT synthesis results in part from alterations in the kinetic properties of tryptophan hydroxylase, perhaps due to calcium-dependent phosphorylation of the enzyme by calmodulin-dependent protein kinase II or cAMP-dependent protein kinase (PKA see Ch. 23). 

Hens started to molt and ceased laying. Feed intake decreased about 90%. Zinc concentrations in pancreas increased 7-fold, in liver 6-fold, kidney 3-fold, and were elevated in shell gland and yolk. High Zn levels in kidney reflect high Zn excretion rates high pancreatic Zn (410 mg Zn/kg FW) may suppress the release of insulin by calmodulin inhibition, and could account for the rapid cessation of lay (Verheyen etal. 1990). 

As explained, the immimomodulation signal starts with binding the antigen on T-cell receptor, which ultimately results in Ca2+ release. Ca2+ induces calmodulin activation, which in turn activates calcineurin, a Ca2+-dependent phosphatase. This event leads to translocation of the cytoplasmic component of the transcription factor, which is required for IL-2 gene expression and T-cell activation. 

As mentioned above, the junctional SR is connected to sheets of perpendicular SR (Fig. 4), which extend from the PM through a peripheral cytoplasmic region with lower myofilament density into the myoplasm. It is proposed that during the active state of wave-like [Ca2+]j oscillations, Ca2+ taken up by the junctional SR is released by these perpendicular sheets near the calmodulin, which is tethered to the myosin light chain kinase (MLCK) of the thin filaments (M. Walsh, personal communication, 2001). This process would enhance the specificity and efficiency of Ca2+ regulation of contraction. 

---