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1.
The selectivity filter of the cation channel TRPM4 总被引:5,自引:0,他引:5
Nilius B Prenen J Janssens A Owsianik G Wang C Zhu MX Voets T 《The Journal of biological chemistry》2005,280(24):22899-22906
Transient receptor potential channel melastatin subfamily (TRPM) 4 and its close homologue, TRPM5, are the only two members of the large transient receptor potential superfamily of cation channels that are impermeable to Ca(2+). In this study, we located the TRPM4 selectivity filter and investigated possible structural elements that render it Ca(2+)-impermeable. Based on homology with known cation channel pores, we identified an acidic stretch of six amino acids in the loop between transmembrane helices TM5 and TM6 ((981)EDMDVA(986)) as a potential selectivity filter. Substitution of this six-amino acid stretch with the selectivity filter of TRPV6 (TIIDGP) resulted in a functional channel that combined the gating hallmarks of TRPM4 (activation by Ca(2+), voltage dependence) with TRPV6-like sensitivity to block by extracellular Ca(2+) and Mg(2+) as well as Ca(2+) permeation. Neutralization of Glu(981) resulted in a channel with normal permeability properties but a strongly reduced sensitivity to block by intracellular spermine. Neutralization of Asp(982) yielded a functional channel that exhibited extremely fast desensitization (tau < 5 s), possibly indicating destabilization of the pore. Neutralization of Asp(984) resulted in a non-functional channel with a dominant negative phenotype when coexpressed with wild type TRPM4. Combined neutralization of all three acidic residues resulted in a functional channel whose voltage dependence was shifted toward very positive potentials. Substitution of Gln(977) by a glutamate, the corresponding residue in divalent cation-permeable TRPM channels, altered the monovalent cation permeability sequence and resulted in a pore with moderate Ca(2+) permeability. Our findings delineate the selectivity filter of TRPM channels and provide the first insight into the molecular basis of monovalent cation selectivity. 相似文献
2.
Topala CN Groenestege WT Thébault S van den Berg D Nilius B Hoenderop JG Bindels RJ 《Cell calcium》2007,41(6):513-523
TRPM6 and its closest relative TRPM7 are members of the Transient Receptor Potential Melastatin (TRPM) subfamily of cation channels and are known to be Mg2+ permeable. By aligning the sequence of the putative TRPM6 pore with the pore sequences of the other subfamily members, we located in the loop between the fifth and the sixth transmembrane domain, a stretch of amino acids residues, 1028GEIDVC1033, as the potential selectivity filter. Two negatively charged residues, E1024 (conserved in TRPM6, TRPM7, TRPM1 and TRPM3) and D1031 (conserved along the entire TRPM subfamily), were identified as important determinants of cation permeation through TRPM6, because neutralization of both residues into an alanine resulted in non-functional channels. Neutralization of E1029 (conserved in TRPM6, TRPM7, TRPM4 and TRPM5) resulted in channels with increased conductance for Ba2+ and Zn2+, decreased ruthenium red sensitivity and larger pore diameter compared to wild-type TRPM6. Changing the residue I1030 into methionine, resulted in channels with lower conductance for Ni2+, decreased sensitivity to ruthenium red block and reduced pore diameter. Thus, these data demonstrate that amino acid residues E1024, I1030 and D1031 are important for channel function and that subtle amino acid variation in the pore region accounts for TRPM6 permeation properties. 相似文献
3.
Molecular and functional characterization of the melastatin-related cation channel TRPM3 总被引:10,自引:0,他引:10
Grimm C Kraft R Sauerbruch S Schultz G Harteneck C 《The Journal of biological chemistry》2003,278(24):21493-21501
Proteins of the mammalian TRP (transient receptor potential) family form a heterogenous group of cation channels important for cellular Ca2+ signaling and homeostasis. Here we present the full-length sequence of TRPM3, a member of the melastatin-like subfamily (TRPM) of TRP channels. TRPM3 expression was found in human kidney and brain. HEK293 cells transiently transfected with TRPM3 showed a constitutive Ca2+ and Mn2+ entry. Whole-cell patch clamp experiments confirmed the spontaneous activity of TRPM3 and revealed permeability ratios PCa/PNa of 1.57 and PNa/PCs of 0.75. In cell-attached patches, spontaneous inward and outward currents were observed. At negative membrane potentials and in the presence of either 140 mm Cs+, 140 mm Na+, or 100 mm Ca2+ in the pipette solution, the single channel conductance levels were 133, 83, and 65 pS, respectively. The Ca2+ entry in TRPM3-expressing HEK293 cells increased during treatment with hypotonic extracellular solution. The reduction of extracellular osmolarity was accompanied by cell swelling, suggesting volume-regulated activity of TRPM3. From its function and expression in human kidney, we propose a role of TRPM3 in renal Ca2+ homeostasis. 相似文献
4.
Nilius B Prenen J Droogmans G Voets T Vennekens R Freichel M Wissenbach U Flockerzi V 《The Journal of biological chemistry》2003,278(33):30813-30820
TRPM4 is a Ca2+-activated but Ca2+-impermeable cation channel. An increase of [Ca2+]i induces activation and subsequent reduction of currents through TRPM4 channels. This inactivation is strikingly decreased in cell-free patches. In whole cell and cell-free configuration, currents through TRPM4 deactivate rapidly at negative potentials. At positive potentials, currents are much larger and activate slowly. This voltage-dependent behavior induces a striking outward rectification of the steady state currents. The instantaneous current-voltage relationship, derived from the amplitude of tail currents following a prepulse to positive potentials, is linear. Currents show a Boltzmann type of activation; the fraction of open channels increases at positive potentials and is low at negative potentials. Voltage dependence is not due to block by divalent cations or to voltage-dependent binding of intracellular Ca2+ to an activator site, indicating that TRPM4 is a transient receptor potential channel with an intrinsic voltage-sensing mechanism. Voltage dependence of TRPM4 may be functionally important, especially in excitable tissues generating plateau-like or bursting action potentials. 相似文献
5.
Nilius B Prenen J Tang J Wang C Owsianik G Janssens A Voets T Zhu MX 《The Journal of biological chemistry》2005,280(8):6423-6433
TRPM4, a Ca(2+)-activated cation channel of the transient receptor potential superfamily, undergoes a fast desensitization to Ca(2+). The mechanisms underlying the alterations in Ca(2+) sensitivity are unknown. Here we show that cytoplasmic ATP reversed Ca(2+) sensitivity after desensitization, whereas mutations to putative ATP binding sites resulted in faster and more complete desensitization. Phorbol ester-induced activation of protein kinase C (PKC) increased the Ca(2+) sensitivity of wild-type TRPM4 but not of two mutants mutated at putative PKC phosphorylation sites. Overexpression of a calmodulin mutant unable to bind Ca(2+) dramatically reduced TRPM4 activation. We identified five Ca(2+)-calmodulin binding sites in TRPM4 and showed that deletion of any of the three C-terminal sites strongly impaired current activation by reducing Ca(2+) sensitivity and shifting the voltage dependence of activation to very positive potentials. Thus, the Ca(2+) sensitivity of TRPM4 is regulated by ATP, PKC-dependent phosphorylation, and calmodulin binding at the C terminus. 相似文献
6.
7.
The sulfonylurea receptor SUR1 associates with Kir6.2 or Kir6.1 to form K(ATP) channels, which link metabolism to excitability in multiple cell types. The strong physical coupling of SUR1 with Kir6 subunits appears exclusive, but recent studies argue that SUR1 also modulates TRPM4, a member of the transient receptor potential family of non-selective cation channels. It has been reported that, following stroke, brain, or spinal cord injury, SUR1 is increased in neurovascular cells at the site of injury. This is accompanied by up-regulation of a non-selective cation conductance with TRPM4-like properties and apparently sensitive to sulfonylureas, leading to the postulation that post-traumatic non-selective cation currents are determined by TRPM4/SUR1 channels. To investigate the mechanistic hypothesis for the coupling between TRPM4 and SUR1, we performed electrophysiological and FRET studies in COSm6 cells expressing TRPM4 channels with or without SUR1. TRPM4-mediated currents were Ca(2+)-activated, voltage-dependent, underwent desensitization, and were inhibited by ATP but were insensitive to glibenclamide and tolbutamide. These properties were not affected by cotransfection with SUR1. When the same SUR1 was cotransfected with Kir6.2, functional K(ATP) channels were formed. In cells cotransfected with Kir6.2, SUR1, and TRPM4, we measured K(ATP)-mediated K(+) currents and Ca(2+)-activated, sulfonylurea-insensitive Na(+) currents in the same patch, further showing that SUR1 controls K(ATP) channel activity but not TRPM4 channels. FRET signal between fluorophore-tagged TRPM4 subunits was similar to that between Kir6.2 and SUR1, whereas there was no detectable FRET efficiency between TRPM4 and SUR1. Our data suggest that functional or structural association of TRPM4 and SUR1 is unlikely. 相似文献
8.
Sites of the NUDT9-H domain critical for ADP-ribose activation of the cation channel TRPM2 总被引:6,自引:0,他引:6
TRPM2 is a cation channel unique within the transient receptor potential family because of its gating by ADP-ribose (ADPR). ADPR gating is enabled by a cytosolic C-terminal Nudix box sequence motif embedded into a region homologous to the NUDT9 ADPR pyrophosphatase. A recently discovered splice variant of TRPM2 (TRPM2-DeltaC) lacks 34 amino acid residues in the NUDT9 domain and is insensitive to ADPR. To analyze in detail which parts of the deleted sequence (DeltaC-stretch) are critical for ADPR gating, we tested mutants that lacked 19, 25, and 29 amino acid residues in the N-terminal part or had amino acid residues substituted in the remaining C-terminal part of the DeltaC-stretch. All of these mutants displayed typical ADPR-induced currents. However, the deletion or substitution of the amino acid residue Asn-1326 immediately downstream of the DeltaC-stretch abrogated ADPR gating. We furthermore analyzed the mutation I1405E/L1406F in the Nudix box of TRPM2, because a considerably decreased AD-PRase activity of the TRPM2 NUDT9-H protein in comparison to the NUDT9 pyrophosphatase has been attributed to the reverse exchange EF --> IL. The I1405E/L1406F variant of TRPM2 failed to respond to ADPR even at concentrations up to 10 mM. We concluded that the DeltaC-stretch contains no individual amino acid residues essential for ADPR gating but may act as a spacer segment stabilizing a conformation necessary for the essential residue Asn-1326 to interact with other channel regions. Enhancing the enzymatic activity of the Nudix box abolishes the ADPR gating of TRPM2, pointing to the requirement of prolonged binding rather than degradation. 相似文献
9.
Nilius B Mahieu F Prenen J Janssens A Owsianik G Vennekens R Voets T 《The EMBO journal》2006,25(3):467-478
Transient receptor potential (TRP) channel, melastatin subfamily (TRPM)4 is a Ca2+-activated monovalent cation channel that depolarizes the plasma membrane and thereby modulates Ca2+ influx through Ca2+-permeable pathways. A typical feature of TRPM4 is its rapid desensitization to intracellular Ca2+ ([Ca2+]i). Here we show that phosphatidylinositol 4,5-biphosphate (PIP2) counteracts desensitization to [Ca2+]i in inside-out patches and rundown of TRPM4 currents in whole-cell patch-clamp experiments. PIP2 shifted the voltage dependence of TRPM4 activation towards negative potentials and increased the channel's Ca2+ sensitivity 100-fold. Conversely, activation of the phospholipase C (PLC)-coupled M1 muscarinic receptor or pharmacological depletion of cellular PIP2 potently inhibited currents through TRPM4. Neutralization of basic residues in a C-terminal pleckstrin homology (PH) domain accelerated TRPM4 current desensitization and strongly attenuated the effect of PIP2, whereas mutations to the C-terminal TRP box and TRP domain had no effect on the PIP2 sensitivity. Our data demonstrate that PIP2 is a strong positive modulator of TRPM4, and implicate the C-terminal PH domain in PIP2 action. PLC-mediated PIP2 breakdown may constitute a physiologically important brake on TRPM4 activity. 相似文献
10.
Calcium-activated nonselective (CAN) cation channels are expressed in various excitable and nonexcitable cells supporting important cellular responses such as neuronal bursting activity, fluid secretion, and cardiac rhythmicity. We have cloned and characterized a second form of TRPM4, TRPM4b, a member of the TRP channel family, as a molecular candidate of a CAN channel. TRPM4b encodes a cation channel of 25 pS unitary conductance that is directly activated by [Ca2+]i with an apparent K(D) of approximately 400 nM. It conducts monovalent cations such as Na+ and K+ without significant permeation of Ca2+. TRPM4b is activated following receptor-mediated Ca2+ mobilization, representing a regulatory mechanism that controls the magnitude of Ca2+ influx by modulating the membrane potential and, with it, the driving force for Ca2+ entry through other Ca2+-permeable pathways. 相似文献
11.
TRPM5 is a voltage-modulated and Ca(2+)-activated monovalent selective cation channel 总被引:8,自引:0,他引:8
The TRPM subfamily of mammalian TRP channels displays unusually diverse activation mechanisms and selectivities. One member of this subfamily, TRPM5, functions in taste receptor cells and has been reported to be activated through G protein-coupled receptors linked to phospholipase C. However, the specific mechanisms regulating TRPM5 have not been described. Here, we demonstrate that TRPM5 is a monovalent-specific cation channel with a 23 pS unitary conductance. TRPM5 does not display constitutive activity. Rather, it is activated by stimulation of a receptor pathway coupled to phospholipase C and by IP(3)-mediated Ca(2+) release. Gating of TRPM5 was dependent on a rise in Ca(2+) because it was fully activated by Ca(2+). Unlike any previously described mammalian TRP channel, TRPM5 displayed voltage modulation and rapid activation and deactivation kinetics upon receptor stimulation. The most closely related protein, the Ca(2+)-activated monovalent-selective cation channel TRPM4b, also showed voltage modulation, although with slower relaxation kinetics than TRPM5. Taken together, the data demonstrate that TRPM5 and TRPM4b represent the first examples of voltage-modulated, Ca(2+)-activated, monovalent cation channels (VCAMs). The voltage modulation and rapid kinetics provide TRPM5 with an excellent set of properties for participating in signaling in taste receptors and other excitable cells. 相似文献
12.
TRPM7 is a divalent cation-permeable channel that is ubiquitously expressed. Recently, mouse TRPM7 has been shown to be sensitive to, and even permeable to, protons when heterologously expressed. Here we have demonstrated that human TRPM7 expressed either heterologously or endogenously also exhibits proton conductivity. The gene silencing of TRPM7 by small interfering RNA suppressed H+ currents in human cervical epithelial HeLa cells. In HEK293T cells transfected with human TRPM7, the inward proton conductance was suppressed by extracellular Mg2+ or Ca2+ with IC(50) values of 0.5 and 1.9 mm, respectively. Anomalous mole fraction behavior of H+ currents in the presence of Mg2+ or Ca2+ indicated that these divalent cations compete with protons for binding sites. Systematic mutation of negatively charged amino acid residues within the putative pore-forming region of human TRPM7 into the neutral amino acid alanine was tested. E1047A resulted in non-functional channels, and D1054A abolished proton conductance, whereas E1052A and D1059A only partially reduced proton conductivity. Thus, it is concluded that Asp-1054 is an essential determinant of the proton conductivity, whereas Glu-1047 might be required for channel formation, and the remaining negatively charged amino acids in the pore region (Glu-1052 and Asp-1059) may play a facilitating role in the proton conductivity of human TRPM7. It is suggested that proton conductivity of endogenous human TRPM7 plays a role in physiologically/pathologically acidic situations. 相似文献
13.
Oike H Wakamori M Mori Y Nakanishi H Taguchi R Misaka T Matsumoto I Abe K 《Biochimica et biophysica acta》2006,1761(9):1078-1084
Vertebrate sensory cells such as vomeronasal neurons and Drosophila photoreceptor cells use TRP channels to respond to exogenous stimuli. In mammalian taste cells, bitter and sweet substances as well as some amino acids are received by G protein-coupled receptors (T2Rs or T1Rs). As a result of activation of G protein and phospholipase Cbeta2, the TRPM5 channel is activated. Intracellular Ca(2+) is known to be a TRPM5 activator, but the participation of lipid activators remains unreported. To clarify the effect of arachidonic acid on TRPM5 in taste cells, we investigated the expression profile of a series of enzymes involved in controlling the intracellular free arachidonic acid level, with the result that in a subset of taste bud cells, monoglyceride lipase (MGL) and cyclooxygenase-2 (COX-2) are expressed as well as the previously reported group IIA phospholipase A(2) (PLA(2)-IIA). Double-labeling analysis revealed that MGL, COX-2 and PLA(2)-IIA are co-expressed in some cells that express TRPM5. We then investigated whether arachidonic acid activates TRPM5 via a heterologous expression system in HEK293 cells, and found that its activation occurred at 10 microM arachidonic acid. These results strongly suggest the possibility that arachidonic acid acts as a modulator of TRPM5 in taste signaling pathways. 相似文献
14.
Oberwinkler J Lis A Giehl KM Flockerzi V Philipp SE 《The Journal of biological chemistry》2005,280(23):22540-22548
TRPM3 is a poorly understood member of the large family of transient receptor potential (TRP) ion channels. Here we describe five novel splice variants of TRPM3, TRPM3alpha1-5. These variants are characterized by a previously unknown amino terminus of 61 residues. The differences between the five variants arise through splice events at three different sites. One of these splice sites might be located in the pore region of the channel as indicated by sequence alignment with other, better-characterized TRP channels. We selected two splice variants, TRPM3alpha1 and TRPM3alpha2, that differ only in this presumed pore region and analyzed their biophysical characteristics after heterologous expression in human embryonic kidney 293 cells. TRPM3alpha1 as well as TRPM3alpha2 induced a novel, outwardly rectifying cationic conductance that was tightly regulated by intracellular Mg(2+). However, these two variants are highly different in their ionic selectivity. Whereas TRPM3alpha1-encoded channels are poorly permeable for divalent cations, TRPM3alpha2-encoded channels are well permeated by Ca(2+) and Mg(2+). Additionally, we found that currents through TRPM3alpha2 are blocked by extracellular monovalent cations, whereas currents through TRPM3alpha1 are not. These differences unambiguously show that TRPM3 proteins constitute a pore-forming channel subunit and localize the position of the ion-conducting pore within the TRPM3 protein. Although the ionic selectivity of ion channels has traditionally been regarded as rather constant for a given channel-encoding gene, our results show that alternative splicing can be a mechanism to produce channels with very different selectivity profiles. 相似文献
15.
Erler I Al-Ansary DM Wissenbach U Wagner TF Flockerzi V Niemeyer BA 《The Journal of biological chemistry》2006,281(50):38396-38404
TRPM (transient receptor potential melastatin-like) channels are distinct from many other members of the transient receptor potential family in regard to their overall size (>1000 amino acids), the lack of N-terminal ankyrin-like repeats, and hydrophobicity predictions that may allow for more than six transmembrane regions. Common to each TRPM member is a prominent C-terminal coiled coil region. Here we have shown that TRPM8 channels assemble as multimers using the putative coiled coil region within the intracellular C terminus and that this assembly can be disturbed by a single point mutation within the coiled coil region. This mutant neither gives rise to functional channels nor do its subunits interact or form protein complexes that correspond to a multimer. However, they are still transported to the plasma membrane. Furthermore, wild-type currents can be suppressed by expressing the membrane-attached C-terminal region of TRPM8. To separate assembly from trafficking, we investigated the maturation of TRPM8 protein by identifying and mutating the relevant N-linked glycosylation site and showing that glycosylation is neither essential for multimerization nor for transport to the plasma membrane per se but appears to facilitate efficient multimerization and transport. 相似文献
16.
Functional characterization of homo- and heteromeric channel kinases TRPM6 and TRPM7 总被引:1,自引:0,他引:1
TRPM6 and TRPM7 are two known channel kinases that play important roles in various physiological processes, including Mg2+ homeostasis. Mutations in TRPM6 cause hereditary hypomagnesemia and secondary hypocalcemia (HSH). However, whether TRPM6 encodes functional channels is controversial. Here we demonstrate several signature features of TRPM6 that distinguish TRPM6 from TRPM7 and TRPM6/7 channels. We show that heterologous expression of TRPM6 but not the mutant TRPM6(S141L) produces functional channels with divalent cation permeability profile and pH sensitivity distinctive from those of TRPM7 channels and TRPM6/7 complexes. TRPM6 exhibits unique unitary conductance that is 2- and 1.5-fold bigger than that of TRPM7 and TRPM6/7. Moreover, micromolar levels of 2-aminoethoxydiphenyl borate (2-APB) maximally increase TRPM6 but significantly inhibit TRPM7 channel activities; whereas millimolar concentrations of 2-APB potentiate TRPM6/7 and TRPM7 channel activities. Furthermore, Mg2+ and Ca2+ entry through TRPM6 is enhanced three- to fourfold by 2-APB. Collectively, these results indicate that TRPM6 forms functional homomeric channels as well as heteromeric TRPM6/7 complexes. The unique characteristics of these three channel types, TRPM6, TRPM7, and TRPM6/7, suggest that they may play different roles in vivo. 相似文献
17.
TRPM2 and TRPM8, closely related members of the transient receptor potential (TRP) family, are cation channels activated by quite different mechanisms. Their transmembrane segments S5 and S6 are highly conserved. To identify common structures in S5 and S6 that govern interaction with the pore, we created a chimera in which the S5-pore-S6 region of TRPM8 was inserted into TRPM2, along with a lysine at each transition site. Currents through this chimera were induced by ADP-ribose (ADPR) in cooperation with Ca(2+). In contrast to wild-type TRPM2 channels, currents through the chimera were carried by Cl(-), as demonstrated in ion substitution experiments using the cation N-methyl-D-glucamine (NMDG) and the anion glutamate. Extracellular NMDG had no effects. The substitution of either intracellular or extracellular Cl(-) with glutamate shifted the reversal potential, decreased the current amplitude and induced a voltage-dependent block relieved by depolarization. The lysine in S6 was responsible for the anion selectivity; insertion of a lysine into corresponding sites within S6 of either TRPM2 or TRPM8 created anion channels that were activated by ADPR (TRPM2 I1045K) or by cold temperatures (TRPM8 V976K). The positive charge of the lysine was decisive for the glutamate block because the mutant TRPM2 I1045H displayed cation currents that were blocked at acidic but not alkaline intracellular pH values. We conclude that the distal part of S6 is crucial for the discrimination of charge. Because of the high homology of S6 in the whole TRP family, this new role of S6 may apply to further TRP channels. 相似文献
18.
McHugh D Flemming R Xu SZ Perraud AL Beech DJ 《The Journal of biological chemistry》2003,278(13):11002-11006
TRPM2 is a member of the melastatin-related TRP (transient receptor potential) subfamily. It is expressed in brain and lymphocytes and forms a cation channel that is activated by intracellular ADP-ribose and associated with cell death. In this study we investigated the calcium dependence of human TRPM2 expressed under a tetracycline-dependent promoter in HEK-293 cells. TRPM2 expression was associated with enhanced hydrogen peroxide-evoked intracellular calcium signals. In whole-cell patch clamp recordings, switching from barium- to calcium-containing extracellular solution markedly activated TRPM2 as long as ADP-ribose was in the patch pipette and exogenous intracellular calcium buffering was minimal. We suggest this effect reveals a critical dependence of TRPM2 channel activity on intracellular calcium. In the absence of extracellular calcium we observed concentration-dependent activation of TRPM2 channels by calcium delivered from the patch pipette (EC(50) 340 nM, slope 4.9); the maximum effect was at least as large as that evoked by extracellular calcium. Intracellular dialysis of cells with high concentrations of EGTA or 1,2-bis(o-Aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) strongly reduced the amplitude of the extracellular calcium response, and the residual response was abolished by a mixture of high and low affinity calcium buffers. TRPM2 channel currents in inside-out patches showed a strong requirement for Ca(2+) at the intracellular face of the membrane. We suggest that calcium entering via TRPM2 proteins acts at an intracellular calcium sensor closely associated with the channel, providing essential positive feedback for channel activation. 相似文献
19.
Murakami M Xu F Miyoshi I Sato E Ono K Iijima T 《Biochemical and biophysical research communications》2003,307(3):522-528
The transient receptor potential (TRP) channels form a superfamily with six transmembrane structures, which is common in other types of voltage-dependent channels. The TRP-melastatin (TRPM) subfamily includes the putative tumor-suppressor melastatin, which was originally found as a down-regulated protein in melanoma tumor cell lines. Here, we report a novel TRP-related protein that is a murine orthologue of human TRPM4. The function of the novel murine TRPM4 was studied in HEK-293 cells using a fluorescent calcium indicator, fura-2. The removal and re-introduction of extracellular calcium triggered changes in the intracellular calcium only in cells expressing TRPM4a, which suggests that this novel channel plays a role in the calcium entry process. We also isolated a splice variant of TRPM4 that was proven to be non-functional. Both TRPM4 variants integrated into the plasma membrane. Furthermore, FRET analysis revealed that TRPM4a and TRPM4b localized close together, suggesting a multimerization of the two molecules. 相似文献
20.
Using the patch-clamp technique, a non-selective voltage-activated Na+ and K+ channel in the human red blood cell membrane was found. The channel operates only at positive membrane potentials from about +30 mV (inside positive) onwards. For sodium and potassium ions, similar conductances of about 21 pS were determined. Together with the recently described K+(Na+)/H+ exchanger, this channel is responsible for the increase of residual K+ and Na+ fluxes across the human red blood cell membrane when the cells are suspended in low ionic strength medium. 相似文献