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Linear Current (linear + current)
Selected AbstractsSingle mechano-gated channels activated by mechanical deformation of acutely isolated cardiac fibroblasts from ratsACTA PHYSIOLOGICA, Issue 3 2010A. Kamkin Abstract Aim:, Mechanosensitive conductances were reported in cardiac fibroblasts, but the properties of single channels mediating their mechanosensitivity remain uncharacterized. The aim of this work was to investigate single mechano-gated channels (MGCs) activated by mechanical deformations of cardiac fibroblasts. Methods:, Currents through single MGCs and mechanosensitive whole-cell currents were recorded from isolated rat atrial fibroblasts using the cell-attached and whole-cell patch-clamp configurations respectively. Defined mechanical stress was applied via the patch pipette used for the whole-cell recordings. Results:, Under resting conditions occasional short openings of two types of single MGCs with conductances of 43 and 87 pS were observed. Both types of channels displayed a linear current,voltage relationship with the reversal potential around 0 mV. Small (1 ,m) mechanical deformations affected neither single nor whole-cell mechano-gated currents. Cell compressions (2, 3 and 4 ,m) augmented the whole-cell currents and increased the frequency and duration of single channel openings. Cell stretches (2, 3 and 4 ,m) inactivated the whole-cell currents and abolished the activity of single MGCs. Gd3+ (8 ,m) blocked the whole-cell currents within 5 min. No single channel activity was observed in the cell-attached mode when Gd3+ was added to the intrapipette solution. Cytochalasin D and colchicine (100 ,m each) completely blocked both the whole-cell and single channel currents. Conclusions:, These findings show that rat atrial fibroblasts express two types of MGCs whose activity is governed by cell deformation. We conclude that fibroblasts can sense the direction of applied stress and contribute to mechano-electrical coupling in the heart. [source] Dominance of the lurcher mutation in heteromeric kainate and AMPA receptor channelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2001Martin K. Schwarz Abstract Homomeric glutamate receptor (GluR) channels become spontaneously active when the last alanine residue within the invariant SYTANLAAF-motif in the third membrane segment is substituted by threonine. The same mutation in the orphan GluR,2 channel is responsible for neurodegeneration in ,Lurcher' (Lc) mice. Since most native GluRs are composed of different subunits, we investigated the effect of an Lc-mutated subunit in heteromeric kainate and AMPA receptors expressed in HEK293 cells. Kainate receptor KA2 subunits, either wild type or carrying the Lc mutation (KA2Lc), are retained inside the cell but are surface-expressed when assembled with GluR6 sununits. Importantly, KA2Lc dominates the gating of KA2Lc/GluR6WT channels, as revealed by spontaneous activation and by slowed desensitization and deactivation kinetics of ligand-activated whole-cell currents. Moreover, the AMPA receptor subunit GluR-BLc(Q) which forms spontaneously active homomeric channels with rectifying current-voltage relationships, dominates the gating of heteromeric GluR-BLc(Q)/GluR-A(R) channels. The spontaneous currents of these heteromeric AMPAR channels show linear current,voltage relationships, and the ligand-activated whole-cell currents display slower deactivation and desensitization kinetics than the respective wild-type channels. For heteromeric Lc-mutated kainate and AMPA receptors, the effects on kinetics were reduced relative to the homomeric Lc-mutated forms. Thus, an Lc-mutated subunit can potentially influence heteromeric channel function in vivo, and the severity of the phenotype will critically depend on the levels of homomeric GluRLc and heteromeric GluRLc/GluRWT channels. [source] Heterogeneity of Kir4.1 channel expression in glia revealed by mouse transgenesisGLIA, Issue 16 2009Xiaofang Tang Abstract The weakly inwardly rectifying K+ channel Kir4.1 is found in many glial cells including astrocytes. However, questions remain regarding the relative contribution of Kir4.1 to the resting K+ conductance of mature astrocytes in situ. We employed a bacterial artificial chromosome transgenic approach in mice to visualize Kir4.1 expression in vivo. These mice (Kir4.1-EGFP) express enhanced green fluorescent protein (EGFP) under the transcriptional control of the Kir4.1 promoter. The brains of adult Kir4.1-EGFP transgenic mice showed co-expression of EGFP and Kir4.1 in astrocytes. In addition, weaker expression of EGFP was detected in NG2+ glial cells when compared with EGFP expression in GFAP+ glial cells. Whole-cell voltage clamp recordings of EGFP+ glial cells in the CA1 area of the adult mouse hippocampus indicated astrocytes displaying properties consistent with both the "passive" and "complex" subpopulations. EGFP+ cells with bright fluorescence had the linear current,voltage (I,V) relationships and extensive gap junctional coupling characteristic of passive astrocytes. However, EGFP+ glia with weaker fluorescence displayed properties associated with complex astrocytes including nonlinear I,V relationships and lack of intercellular gap junctional coupling. Pharmacological blockade of inward currents implied that Kir4.1 channels constitute the dominant resting K+ conductance in both glial cell types and are more highly expressed in passive astrocytes. These results suggest differential expression of Kir4.1 in glia and that this channel likely underlies the resting K+ conductance in passive and complex astrocytes. © 2009 Wiley-Liss, Inc. [source] Studies on the mechanisms of action of picrotoxin, quercetin and pregnanolone at the GABA,1 receptorBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2004Juan D Goutman The mechanisms of action of antagonists of the , -aminobutyric acid C (GABAC) receptor picrotoxin, quercetin and pregnanolone were studied. Ionic currents (chloride), mediated through human homomeric GABA,1 receptors expressed in Xenopus oocytes, were recorded by two-electrode voltage clamp. Dose,response (D,R) curves and kinetic measurements of GABA,1 currents were carried out in the presence or absence of antagonists. Use-dependent actions were also evaluated. Picrotoxin, quercetin and pregnanolone exerted noncompetitive actions. IC50 values measured at the EC50 for GABA (1 ,M) were as follows: picrotoxin 0.6±0.1 ,M (Hill coefficient n=1.0±0.2); quercetin 4.4±0.4 ,M (n=1.5±0.2); pregnanolone 2.1±0.5 ,M (n=0.8±0.1). These antagonists produced changes only in the slope of the linear current,voltage relationships, which was indicative of voltage-independent effects. The effect of picrotoxin on GABA,1 currents was use-dependent, strongly relied on agonist concentration and showed a slow onset and offset. The mechanism was compatible with an allosteric inhibition and receptor activation was a prerequisite for antagonism. The effect of quercetin was use-independent, showed relatively fast onset and offset, and resulted in a slowed time course of the GABA-evoked currents. The effect of pregnanolone was use-independent, presented fast onset and a very slow washout, and did not affect current activation. All the antagonists accelerated the time course of deactivation of the GABA,1 currents. British Journal of Pharmacology (2004) 141, 717,727. doi:10.1038/sj.bjp.0705657 [source] | ||||||||||