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_6 label "Selventa" provenance.
_5 value "Chloride channels, like Na+ channels, are more frequently activated by cytochalasin and inactivated by increasing actin cross linking, but again, there are exceptions to a simple interpretation, since F-actin itself can also activate some Cl channel activity. In several cases where the effects of cytochalasin have been compared with those of nocodazole or colchicine, microtubule disruption has not been found to affect Na+, K+, or Cl channels. However, disruption of microtubules has been reported to enhance the activity of both Ca2+ (73, 218) and Cl (92, 109) channels in some cases. An intriguing hypothesis for how disruption of actin may activate K+ channels is by release of protein kinase A (PKA) bound to the actin (175). In this model, the regulation depends not only on a link of actin to the receptor, but on changing localization of a cytoskeleton-bound signaling kinase, as discussed in section IIB. Some Ca2+ channels are inactivated by cytochalasin, and the effect is blocked by phalloidin. However, stretch-activated Ca2+ influx can be activated by cytochalasin and inhibited by F-actin. Moreover, there are several reports of microtubule disruption also altering Ca2+ channel activity (73, 218), with a strong enhancement in one case that was not achieved by cytochalasin. A scenario derived from Reference 78 for how actin filaments may affect Ca2+ influx resulting from mechanical stresses is shown in Figure 2. In this model, application of a mechanical stress at the plasma membrane of a resting cell causes deformation of channels in the plasma membrane that results in Ca2+ influx. In these cells, a sustained mechanical stress leads to assembly of two distinct structures: contractile elements containing actin filaments that create an opposing force and an elastic network that resists subsequent application of the external stress. As the stress is transmitted to the newly formed three-dimensional cytoskeleton, it is directed away from the plasma membrane, and the deformation of membrane elements near the site of force is now insufficient to activate Ca2+ influx. One context in which mechanical effects on the cytoskeleton regulate ion fluxes is volume regulation after osmotic stress. Although the elastic modulus of the cytoskeleton is probably too low (1,000-10,000 Pa in some cell types and lower in others) to prevent volume changes caused by osmotic imbalance (10,000 Pa/mosM), its presence as an elastic element provides the cell with a countering tension and a memory of the undeformed state, at least for the time that the cross-linked cytoskeleton remains intact. It is not surprising, therefore, that the cytoskeleton affects ion transport in volume regulation (33, 43, 92, 129, 193). Among the clearest evidence for a mechanical function comes from the finding that melanoma cells containing approximately normal amounts of cytoskeletal filaments and ion channels, but lacking the cross-linking protein ABP280 that provides rigidity to the cell cortex, fail to volume regulate under hypotonic conditions. Transfection of ABP280 to these cells restores this capacity (33). Whether the effects of the cytoskeleton on ion channel activity are a direct mechanical effect or an indirect effect due to such changes as regulation of kinases sequestered at the cytoskeleton remains a controversial issue. There are reports that the cytoskeleton has no effect on channel activity and reports that ion conductance through channels within a lipid bilayer can be altered by bilayer dilation in the absence of any internal network (162). On the other hand, there are intriguing hypotheses that actin filaments and microtubules could directly transmit ion fluxes because of their polyelectrolyte nature and the presence of a condensed counterion cloud (133). Although such effects appear plausible from a physical-chemical perspective, demonstrating their importance in biological ion signaling remains a chal..." provenance.
_5 wasQuotedFrom 9674694 provenance.
assertion hadPrimarySource 9674694 provenance.
large_corpus.bel title "BEL Framework Large Corpus Document" provenance.
large_corpus.bel description "Approximately 61,000 statements." provenance.
assertion wasDerivedFrom large_corpus.bel provenance.
assertion wasDerivedFrom _5 provenance.
large_corpus.bel authoredBy _6 provenance.
large_corpus.bel version "20131211" provenance.