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Membrane Ca2+ (membrane + ca2+)
Kinds of Membrane Ca2+ Terms modified by Membrane Ca2+ Selected AbstractsPlasma membrane Ca2+ -ATPase in the cilia of olfactory receptor neurons: possible role in Ca2+ clearanceEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2007Karen Castillo Abstract Olfactory sensory neurons respond to odorants increasing Ca2+ concentrations in their chemosensory cilia. Calcium enters the cilia through cAMP-gated channels, activating Ca2+ -dependent chloride or potassium channels. Calcium also has a fundamental role in odour adaptation, regulating cAMP turnover rate and the affinity of the cyclic nucleotide-gated channels for cAMP. It has been shown that a Na+/Ca2+ exchanger (NCX) extrudes Ca2+ from the cilia. Here we confirm previous evidence that olfactory cilia also express plasma membrane Ca2+ -ATPase (PMCA), and show the first evidence supporting a role in Ca2+ removal. Both transporters were detected by immunoblot of purified olfactory cilia membranes. The pump was also revealed by immunocytochemistry and immunohistochemistry. Inside-out cilia membrane vesicles transported Ca2+ in an ATP-dependent fashion. PMCA activity was potentiated by luminal Ca2+ (K0.5 = 670 nm) and enhanced by calmodulin (CaM; K0.5 = 31 nm). Both carboxyeosin (CE) and calmidazolium reduced Ca2+ transport, as expected for a CaM-modulated PMCA. The relaxation time constant (,) of the Ca2+ -dependent Cl, current (272 ± 78 ms), indicative of luminal Ca2+ decline, was increased by CE (2181 ± 437 ms), by omitting ATP (666 ± 49 ms) and by raising pH (725 ± 65 ms), suggesting a role of the pump on Ca2+ clearance. Replacement of external Na+ by Li+ had a similar effect (, = 442 ± 8 ms), confirming the NCX involvement in Ca2+ extrusion. The evidence suggests that both Ca2+ transporters contribute to re-establish resting Ca2+ levels in the cilia following olfactory responses. [source] No evidence for calcium electrogenic exchanger in frog semicircular canal hair cellsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2002M. Martini Abstract We investigated the possibility that, in hair cells mechanically isolated from frog semicircular canals, Ca2+ extrusion occurs via a Na+ : Ca2+ (cardiac type) or a Na+ : Ca2+,K+ (retinal type) exchanger. Cells concurrently imaged during whole-cell patch-clamp recordings using the Ca2+ sensitive fluorescent dye Oregon Green 488 BAPTA-1 (100 µm) showed no voltage dependence of Ca2+ clearance dynamics following a Ca2+ load through voltage-gated Ca2+ channels. Reverse exchange was probed in hair cells dialyzed with a Ca2+ - and K+ -free solution, containing a Na+ concentration that saturates the exchanger, after zeroing the contribution to the whole-cell current from Ca2+ and K+ conductances. In these conditions, no reverse exchange current was detected upon switching from a Ca2+ -free external solution to a solution containing concentrations of Ca2+ alone, or Ca2+ + K+ that saturated the exchanger. By contrast, the same experimental protocol elicited peak exchange currents exceeding 100 pA in gecko rod photoreceptors, used as positive controls. In both cell types, we also probed the forward mode of the exchanger by rapidly increasing the intracellular Ca2+ concentration using flash photolysis of two novel caged Ca2+ complexes, calcium 2,2,-{[1-(2-nitrophenyl)ethane-1,2-diyl]bis(oxy)}bis(acetate) and calcium 2,2,-{[1-(4,5-dimethoxy-2-nitrophenyl)ethane-1,2-diyl]bis(oxy)} bis(acetate), in the presence of internal K+ and external Na+. No currents were evoked by UV-triggered Ca2+ jumps in hair cells, whereas exchanger conformational currents up to 400 pA, followed by saturating forward exchange currents up to 40 pA, were recorded in rod photoreceptors subjected to the same experimental conditions. We conclude that no functional electrogenic exchanger is present in this hair cell population, which leaves the abundant plasma membrane Ca2+ -ATPases as the primary contributors to Ca2+ extrusion. [source] Partitioning of the plasma membrane Ca2+ -ATPase into lipid rafts in primary neurons: effects of cholesterol depletionJOURNAL OF NEUROCHEMISTRY, Issue 2 2007Lei Jiang Abstract Spatial and temporal alterations in intracellular calcium [Ca2+]i play a pivotal role in a wide array of neuronal functions. Disruption in Ca2+ homeostasis has been implicated in the decline in neuronal function in brain aging and in neurodegenerative disorders. The plasma membrane Ca2+ -ATPase (PMCA) is a high affinity Ca2+ transporter that plays a crucial role in the termination of [Ca2+]i signals and in the maintenance of low [Ca2+]i essential for signaling. Recent evidence indicates that PMCA is uniquely sensitive to its lipid environment and is stimulated by lipids with ordered acyl chains. Here we show that both PMCA and its activator calmodulin (CaM) are partitioned into liquid-ordered, cholesterol-rich plasma membrane microdomains or ,lipid rafts' in primary cultured neurons. Association of PMCA with rafts was demonstrated in preparations isolated by sucrose density gradient centrifugation and in intact neurons by confocal microscopy. Total raft-associated PMCA activity was much higher than the PMCA activity excluded from these microdomains. Depletion of cellular cholesterol dramatically inhibited the activity of the raft-associated PMCA with no effect on the activity of the non-raft pool. We propose that association of PMCA with rafts represents a novel mechanism for its regulation and, consequently, of Ca2+ signaling in the central nervous system. [source] Modulation of calcium entry and glutamate release in cultured cerebellar granule cells by palytoxinJOURNAL OF NEUROSCIENCE RESEARCH, Issue 8 2006Carmen Vale Abstract A channel open on the membrane can be formed by palytoxin (PTX). Ten nanomolar PTX caused an irreversible increase in the cytosolic calcium concentration ([Ca2+]c), which was abolished in the absence of external calcium. The increase was eliminated by saxitoxin (STX) and nifedipine (NIF). Calcium rise is secondary to the membrane depolarization. PTX effect on calcium was dependent on extracellular Na+. Li+ decreased the PTX-evoked rise in [Ca2+]c; replacement of Na+ by N-methyl-D-glucamine (NMDG) abolished PTX-induced calcium increase. [Ca2+]c increase by PTX was strongly reduced after inhibition of the reverse operation of the Na+/Ca2+ exchanger, in the presence of antagonists of excitatory amino acid (EAA) receptors, and by inhibition of neurotransmitter release. PTX did not modify calcium extrusion by the plasma membrane Ca2+ -ATPase (PMCA), because blockade of the calcium pump increased rather than decreased the PTX-induced calcium influx. Extracellular levels of glutamate and aspartate were measured by HPLC and exocytotic neurotransmitter release by determination of synaptic vesicle exocytosis using total internal reflection fluorescence microscopy (TIRFM). PTX caused a concentration-dependent increase in EAA release to the culture medium. Ten nanomolar PTX decreased cell viability by 30% within 5 min. PTX-induced calcium influx involves three pathways: Na+ -dependent activation of voltage-dependent sodium channels (VDSC) and voltage-dependent calcium channels (VDCC), reverse operation of the Na+/Ca2+ exchanger, and indirect activation of EAA receptors through glutamate release. The neuronal injury produced by the toxin could be partially mediated by the PTX-induced overactivation of EAA receptors, VDSC, VDCC and the glutamate efflux into the extracellular space. © 2006 Wiley-Liss, Inc. [source] Plant extracellular ATP signalling by plasma membrane NADPH oxidase and Ca2+ channelsTHE PLANT JOURNAL, Issue 6 2009Vadim Demidchik Summary Extracellular ATP regulates higher plant growth and adaptation. The signalling events may be unique to higher plants, as they lack animal purinoceptor homologues. Although it is known that plant cytosolic free Ca2+ can be elevated by extracellular ATP, the mechanism is unknown. Here, we have studied roots of Arabidopsis thaliana to determine the events that lead to the transcriptional stress response evoked by extracellular ATP. Root cell protoplasts were used to demonstrate that signalling to elevate cytosolic free Ca2+ is determined by ATP perception at the plasma membrane, and not at the cell wall. Imaging revealed that extracellular ATP causes the production of reactive oxygen species in intact roots, with the plasma membrane NADPH oxidase AtRBOHC being the major contributor. This resulted in the stimulation of plasma membrane Ca2+ -permeable channels (determined using patch-clamp electrophysiology), which contribute to the elevation of cytosolic free Ca2+. Disruption of this pathway in the AtrbohC mutant impaired the extracellular ATP-induced increase in reactive oxygen species (ROS), the activation of Ca2+ channels, and the transcription of the MAP kinase3 gene that is known to be involved in stress responses. This study shows that higher plants, although bereft of purinoceptor homologues, could have evolved a distinct mechanism to transduce the ATP signal at the plasma membrane. [source] Inhibition of ion transport ATPases by HNEBIOFACTORS, Issue 1-4 2005C. Crifò Abstract 4-Hydroxy-2,3- trans -nonenal (HNE), a major lipid peroxidation product, has been shown to react with specific amino acid residues of proteins and alter their function. In vitro exposure of erythrocyte ghosts and neutrophil membranes to HNE results in the inhibition of ion transport ATPases. Neutrophil membrane Ca2+ -ATPase is strongly inhibited by micromolar concentrations of HNE, while HNE is considerably less effective against neutrophil Mg2+ -ATPase and the erythrocyte ghost enzymes. [source] Antagonist effect of flufenamic acid on TRPM2 cation channels activated by hydrogen peroxideCELL BIOCHEMISTRY AND FUNCTION, Issue 4 2007Mustafa Naz Abstract The melastatin-related transient receptor potential channel TRPM2 is a plasma membrane Ca2+ -permeable cation channel that is activated by hydrogen peroxide (H2O2) as a consequence of oxidative stress although the channel activation by H2O2 appears to represent a cell-specific process in cells with endogenous expression of TRPM2. Flufenamic acid (FA) is a non-steroidal anti-inflammatory compound. Whether H2O2 activates or FA inhibits TRPM2 channels in Chinese hamster ovary (CHO) cell is currently unknown. Due to lack of known antogonists of this channel, we demonstrate in CHO cells that FA inhibits TRPM2 activated by extracellular H2O2. CHO cells were transfected with cDNA coding for TRPM2. Cells were studied with the conventional whole-cell patch clamp technique. The intracellular solution used EDTA (10,mM) as chelator for Ca2+ and heavy metal ions. H2O2 (10,mM) and FA (0.1,mM) were applied extracellularly. Non-selective cation currents were consistently induced by H2O2. The time cause of H2O2 effects was characterized by a delay of 2,5,min and a slow current induction to reach a plateau. The H2O2 - induced inward current was effectively inhibited by 0.1,mM FA applied extracellularly. In conclusion, we have demonstrated that FA is an effective antogonist of TRPM2 channels and H2O2activated currents in CHO cells. FA in CHO cells may be considered, at best, a starting point for the development of TRPM2 channel blockers. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||