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1.
Single water fibers of the frog glossopharyngeal nerve respondto low concentrations of CaCl2 (12 mM) and to relativelyhigh concentrations of NaCl(>80 mM). However, stimulationby a mixture with a low concentration of CaCl2 and relativelyhigh concentration of NaCl gives rise to only a small response,suggesting that the effects of Ca2+ and Na+ are mutually antagonistic.It has been reported that Na+ inhibits the response to Ca2+by competing with Ca2+ for a calcium receptor site (XCa; Kitadaand Shimada, 1980). In the present study, it was found tha Ca2+inhibited the response to Na+. Therefore, the sodium receptorsite (XNa) responsible for the response to Na is different fromXCa. The inhibition of the response to Na+ by Ca2+ was examinedquantitatively on the assumption that the magnitude of the neuralresponse is proportinal to the amount of NaXNa complex minusa constant (the threshold concentration of the NaXNa complex).The results obtained indicate that Ca2+ competes with Na+ forXNa. The apparent dissociation constants for the NaXNa complexand the CaXNa complex obtained from the present study were 1.0M and 1.2 x 10-3 M, respectively, XNa as proposed here, doesnot represent simply a binding site for cations since therecan be competition for XNa by an antagonistie cation. The highaffinity of XNa for Ca2+ suggests that XNa is a specific receptorsite involved in salt-taste reception. Since Mg2+ did not affectthe response to Na+, the affinity of XNa for cations is notcharge-specific but is, rather, chemically specific. The presentresults indicate that both Ca2+ and Na+ have a dual action,being involved both in excitation and in inhibition, in waterfibers of the frog glossopharyngeal nerve. 相似文献
2.
Shibata T Hibino H Doi K Suzuki T Hisa Y Kurachi Y 《American journal of physiology. Cell physiology》2006,291(5):C1038-C1048
Cochlear endolymph has a highly positive potential of approximately +80 mV known as the endocochlear potential (EP). The EP is essential for hearing and is maintained by K+ circulation from perilymph to endolymph through the cochlear lateral wall. Various K+ transport apparatuses such as the Na+,K+-ATPase, the Na+-K+-2Cl cotransporter, and the K+ channels Kir4.1 and KCNQ1/KCNE1 are expressed in the lateral wall and are known to play indispensable roles in cochlear K+ circulation. The gastric type of the H+,K+-ATPase was also shown to be expressed in the cochlear lateral wall (Lecain E, Robert JC, Thomas A, and Tran Ba Huy P. Hear Res 149: 147154, 2000), but its functional role has not been well studied. In this study we examined the precise localization of H+,K+-ATPase in the cochlea and its involvement in formation of EP. RT-PCR analysis showed that the cochlea expressed mRNAs of gastric 1-, but not colonic 2-, and -subunits of H+,K+-ATPase. Immunolabeling of an antibody specific to the 1 subunit was detected in type II, IV, and V fibrocytes distributed in the spiral ligament of the lateral wall and in the spiral limbus. Strong immunoreactivity was also found in the stria vascularis. Immunoelectron microscopic examination exhibited that the H+,K+-ATPase was localized exclusively at the basolateral site of strial marginal cells. Application of Sch-28080, a specific inhibitor of gastric H+,K+-ATPase, to the spiral ligament as well as to the stria vascularis caused prominent reduction of EP. These results may imply that the H+,K+-ATPase in the cochlear lateral wall is crucial for K+ circulation and thus plays a critical role in generation of EP. hydrogen, potassium-adenosine triphosphatase; stria vascularis; spiral ligament 相似文献
3.
Castagna M Soragna A Mari SA Santacroce M Betté S Mandela PG Rudnick G Peres A Sacchi VF 《American journal of physiology. Cell physiology》2007,293(4):C1286-C1295
KAAT1 is a lepidopteran neutral amino acid transporter belonging to the NSS super family (SLC6), which has an unusual cation selectivity, being activated by K+ and Li+ in addition to Na+. We have previously demonstrated that Asp338 is essential for KAAT1 activation by K+ and for the coupling of amino acid and driver ion fluxes. By comparing sequences of NSS family members, site-directed mutagenesis, and expression in Xenopus laevis oocytes, we identified Lys102 as a residue likely to interact with Asp338. Compared with wild type, the single mutants K102V and D338E each showed altered leucine uptake and transport-associated currents in the presence of both Na+ and K+. However, in K102V/D338E double mutant, the K102V mutation reversed both the inhibition of Na+-dependent transport and the block in K+-dependent transport that characterize the D338E mutant. K+-dependent leucine currents were not observed in any mutants with D338E. In the presence of the oxidant Cu(II) (1,10-phenanthroline)3, we observed specific and reversible inhibition of K102C/D338C mutant, but not of the corresponding single cysteine mutants, suggesting that these residues are sufficiently close to form a disulfide bond. Thus both structural and functional evidence suggests that these two residues interact. Similar results have been obtained mutating the bacterial transporter homolog TnaT. Asp338 corresponds to Asn286, a residue located in the Na+ binding site in the recently solved crystal structure of the NSS transporter LeuTAa (41). Our results suggest that Lys102, interacting with Asp338, could contribute to the spatial organization of KAAT1 cation binding site and permeation pathway. residue interaction; oxidants; tertiary structure 相似文献
4.
Two processes of the K+ channel activation in plasma membraneexcitation are suggested for Nitella axilliformis. One is relatedto the repolarizing process in the action potential and theother to the after-hyperpolarization (AH). Extra- and intracellulartetraethylammonium (TEA+) and extracellular Co2+ prolonged theaction potential, indicating involvement of K+ channel activationin the repolarizing process of the action potential. The following findings showed that AH is caused by K+ channelactivation. First, AH was inhibited by extracellular K+ andRb+ but not by Na+ and Li+. Second, it was not inhibited byintracellular TEA+ but by extracellular TEA+. Third, the membraneconductance increased during AH. Generation of AH was dependenton the level of the resting membrane potential [(Em)rest] whichis affected by the activity of the electrogenic H+ pump. AHwas generated, when (Em)rest was more positive than a criticalvalue, which was supposed to be the equilibrium potential forK+ across the plasma membrane. Since extracellular Ca2+ competed with extracellular TEA+ andCo2+ in prolonging the action potential, and sometimes in inhibitingAH, Ca2+ may be involved in the K+ channel activation. (Received June 11, 1983; Accepted September 21, 1983) 相似文献
5.
Insulin stimulates K+ transport by theNa+-K+-ATPase in human fibroblasts. In othercell systems, this action represents an automatic response to increasedintracellular [Na+] or results from translocation oftransporters from an intracellular site to the plasma membrane. Here weevaluate whether these mechanisms are operative in human fibroblasts.Human fibroblasts expressed the 1 but not the2 and 3 isoforms ofNa+-K+-ATPase. Insulin increased the influx ofRb+, used to trace K+ entry, but did not modifythe total intracellular content of K+, Rb+, andNa+ over a 3-h incubation period. Ouabain increasedintracellular Na+ more rapidly in cells incubated withinsulin, but this increase followed insulin stimulation ofRb+ transport. Bumetanide did not prevent the increasedNa+ influx or stimulation ofNa+-K+-ATPase. Stimulation of theNa+-K+- ATPase by insulin did not produce anymeasurable change in membrane potential. Insulin did not affect theaffinity of the pump toward internal Na+ or the number ofmembrane-bound Na+-K+-ATPases, as assessed byouabain binding. By contrast, insulin slightly increased the affinityof Na+-K+-ATPase toward ouabain. Phorbol estersdid not mimic insulin action on Na+-K+-ATPaseand inhibited, rather than stimulated, Rb+ transport. Theseresults indicate that insulin increases the turnover rate ofNa+-K+-ATPases of human fibroblasts withoutaffecting their number on the plasma membrane or modifying theirdependence on intracellular [Na+]. 相似文献
6.
Using the compartmental analysis the unidirectional Na+ fluxesin cortical cells of barley roots, the cytoplasmic and vacuolarNa+ contents Qc and Qv, and the trans-root Na+ transport R'have been studied as a function of the external Na+ concentration.Using the re-elution technique the effect of low K+ concentrationson the plasmalemma efflux co of Na+ (K+-Na+ exchange) and onR' was investigated at different Na+ concentrations and correspondinglydifferent values of the cytoplasmic sodium content Qc. The relationof the K+-dependent Na+ efflux coK+-dep to Qc or to the cytoplasmicNa+ concentration obeyed Michaelis-Menten kinetics. This isconsistent with a linkage of co, K+-dep to K+ influx by a K+-Na+exchange system. The apparent Km corresponded to a cytoplasmicNa+ concentration of 28 mM at 0·2 mM K+ and about 0·2mM Na+ in the external solution. 0·2 mM K+ stimulatedthe plasma-lemma efflux of Na+ and inhibited Na+ transport selectivelyeven in the presence of 10 mM Na+ in the external medium showingthe high efficiency of the K+-Na+ exchange system. However,co, K+-dep was inhibited at 10 mM Na1 compared to lower Na1concentrations suggesting some competition of Na1 with K1 atthe external site of the exchange system. The effect of theNa+ concentration on Na1 influx oc is discussed with respectto kinetic models of uuptake. 相似文献
7.
Hansen PS Clarke RJ Buhagiar KA Hamilton E Garcia A White C Rasmussen HH 《American journal of physiology. Cell physiology》2007,292(3):C1070-C1077
The effect of diabetes on sarcolemmal Na+-K+ pump function is important for our understanding of heart disease associated with diabetes and design of its treatment. We induced diabetes characterized by hyperglycemia but no other major metabolic disturbances in rabbits. Ventricular myocytes isolated from diabetic rabbits and controls were voltage clamped and internally perfused with the whole cell patch-clamp technique. Electrogenic Na+-K+ pump current (Ip, arising from the 3:2 Na+-to-K+ exchange ratio) was identified as the shift in holding current induced by Na+-K+ pump blockade with 100 µmol/l ouabain in most experiments. There was no effect of diabetes on Ip recorded when myocytes were perfused with pipette solutions containing 80 mmol/l Na+ to nearly saturate intracellular Na+-K+ pump sites. However, diabetes was associated with a significant decrease in Ip measured when pipette solutions contained 10 mmol/l Na+. The decrease was independent of membrane voltage but dependent on the intracellular concentration of K+. There was no effect of diabetes on the sensitivity of Ip to extracellular K+. Pump inhibition was abolished by restoration of euglycemia or by in vivo angiotensin II receptor blockade with losartan. We conclude that diabetes induces sarcolemmal Na+-K+ pump inhibition that can be reversed with pharmacological intervention. sodium transport; insulin; angiotensin II; cardiomyopathy; hyperglycemia 相似文献
8.
Tepperman Katherine; Millette Lauren A.; Johnson Carl L.; Jewell-Motz Elizabeth A.; Lingrel Jerry B.; Wallick Earl T. 《American journal of physiology. Cell physiology》1997,273(6):C2065
A competition assay of86Rb+uptake in HeLa cells transfected with ouabain-resistantNa+-K+-ATPasemutants revealed a stimulation of86Rb+uptake at low external concentrations (1 mM) of competitor(K+). Of the models that weretested, those that require that two K+ be bound before transportoccurs gave the worst fits. Random and ordered binding schemesdescribed the data equally well. General models in which both bindingand transport were allowed to be cooperative yielded parameter errorslarger than the parameters themselves and could not be utilized. Modelsthat assumed noncooperative transport always showed positivecooperativity in binding. E327Q and E327L mutated forms of rat2 had lower apparent affinities for the first K+ bound than didwild-type rat 2 modified to beouabain resistant. The mutations did not affect the apparent affinityof the second K+ bound. Modelsthat assumed noncooperativity in binding always showed positivelycooperative transport, i.e., enzymes with two K+ bound had a higher flux thanthose with one K+ bound. Increasesin external Na+ decreased theapparent affinity for K+ for allmodels and decreased the ratio of the apparent influx rate constantsfor E327L. 相似文献
9.
Dependence of Na+-K+ pump current-voltage relationship on intracellular Na+, K+, and Cs+ in rabbit cardiac myocytes 总被引:2,自引:0,他引:2
Hansen PS Buhagiar KA Kong BY Clarke RJ Gray DF Rasmussen HH 《American journal of physiology. Cell physiology》2002,283(5):C1511-C1521
To examine effects of cytosolicNa+, K+, and Cs+ on the voltagedependence of the Na+-K+ pump, we measuredNa+-K+ pump current (Ip)of ventricular myocytes voltage-clamped at potentials(Vm) from 100 to +60 mV. Superfusates weredesigned to eliminate voltage dependence at extracellular pump sites.The cytosolic compartment of myocytes was perfused with patch pipette solutions with a Na+ concentration ([Na]pip)of 80 mM and a K+ concentration from 0 to 80 mM or withsolutions containing Na+ in concentrations from 0.1 to 100 mM and K+ in a concentration of either 0 or 80 mM. When[Na]pip was 80 mM, K+ in pipette solutionshad a voltage-dependent inhibitory effect on Ipand induced a negative slope of theIp-Vm relationship. Cs+ in pipette solutions had an effect onIp qualitatively similar to that ofK+. Increases in Ip with increasesin [Na]pip were voltage dependent. The dielectriccoefficient derived from[Na]pip-Ip relationships at thedifferent test potentials was 0.15 when pipette solutions included 80 mM K+ and 0.06 when pipette solutions were K+ free. 相似文献
10.
Alan C. Swann 《Archives of biochemistry and biophysics》1983,221(1):148-157
The effects of temperature on interactions between univalent cations or ATP and the p-nitrophenylphosphatase activity associated with brain (Na+,K+)-ATPase were examined. The apparent affinity for K+ activation under conditions favoring the moderate affinity site was temperature dependent, increasing with decreasing temperature. A comparison of univalent cations showed that the negative apparent ΔH and ΔS for cation binding increased with increasing apparent cation affinity. In contrast to the case with the moderate affinity sites, apparent affinity for the high affinity K+ site was independent of temperature. As temperature decreased, properties of moderate affinity site binding approached those of the high affinity site. The temperature dependence of ATP inhibition was opposite to that for K+ activation, with positive apparent ΔH and ΔS. The apparent ΔH and ΔS for cation binding approached those for the overall conformational change to K+-sensitive enzyme as cation affinity increased. These data suggest that E2, the K+-sensitive form of (Na+,K+)-ATPase, is stabilized by forces that require a decrease in entropy, explaining the predominant existence of E1 at physiologic temperatures. A conformational change leading to stabilization of E2 at higher temperatures can be produced by binding of univalent cations to a moderate affinity, presumably intracellular, site. This effect is counteracted by ATP. ATP also appears to alter the selectivity of this site to favor Na+ over K+ binding. 相似文献
11.
Dietary cholesterol alters Na+/K+ selectivity at intracellular Na+/K+ pump sites in cardiac myocytes 总被引:1,自引:0,他引:1
Buhagiar KA Hansen PS Kong BY Clarke RJ Fernandes C Rasmussen HH 《American journal of physiology. Cell physiology》2004,286(2):C398-C405
A modest diet-induced increase in serum cholesterol in rabbits increases the sensitivity of the sarcolemmal Na+/K+ pump to intracellular Na+, whereas a large increase in cholesterol levels decreases the sensitivity to Na+. To examine the mechanisms, we isolated cardiac myocytes from controls and from rabbits with diet-induced increases in serum cholesterol. The myocytes were voltage clamped with the use of patch pipettes that contained osmotically balanced solutions with Na+ in a concentration of 10 mM and K+ in concentrations ([K+]pip) ranging from 0 to 140 mM. There was no effect of dietary cholesterol on electrogenic Na+/K+ current (Ip) when pipette solutions were K+ free. A modest increase in serum cholesterol caused a [K+]pip-dependent increase in Ip, whereas a large increase caused a [K+]pip-dependent decrease in Ip. Modeling suggested that pump stimulation with a modest increase in serum cholesterol can be explained by a decrease in the microscopic association constant KK describing the backward reaction E1 + 2K+ E2(K+)2, whereas pump inhibition with a large increase in serum cholesterol can be explained by an increase in KK. Because hypercholesterolemia upregulates angiotensin II receptors and because angiotensin II regulates the Na+/K+ pump in cardiac myocytes in a [K+]pip-dependent manner, we blocked angiotensin synthesis or angiotensin II receptors in vivo in cholesterol-fed rabbits. This abolished cholesterol-induced pump inhibition. Because the -isoform of protein kinase C (PKC) mediates effects of angiotensin II on the pump, we included specific PKC-blocking peptide in patch pipette filling solutions. The peptide reversed cholesterol-induced pump inhibition. partial reactions; protein kinase C; angiotensin converting enzyme inhibitors; arteriosclerosis; insulin resistance 相似文献
12.
The interactions of divalent cations with the adenosine triphosphatase (ATPase) and para-nitrophenyl phosphatase (pNPPase) activity of the purified dog kidney Na pump and the fluorescence of fluorescein isothiocyanate
(FITC)-labeled pump were determined. Sr2+ and Ba2+ did not compete with K+ for ATPase (an extracellular K+ effect). Sr2+ and Ba2+ did compete with Na+ for ATPase (an intracellular Na+ effect) and with K+ for pNPPase (an intracellular K+ effect). These results suggest that Ba2+ or Sr2+ can bind to the intracellular transport site, yet neither Ba2+ nor Sr2+ was able to activate pNPPase activity; we confirmed that Ca2+ and Mn2+ did activate. As another measure of cation binding, we observed that Ca2+ and Mn2+, but not Ba2+, decreased the fluorescence of the FITC-labeled pump; we confirmed that K+ substantially decreased the fluorescence. Interestingly, Ba2+ did shift the K+ dose-response curve. Ethane diamine inhibited Mn2+ stimulation of pNPPase (as well as K+ and Mg2+ stimulation) but did not shift the 50% inhibitory concentration (IC50) for the Mn2+-induced fluorescence change of FITC, though it did shift the IC50 for the K+-induced change. These results suggest that the Mn2+-induced fluorescence change is not due to Mn2+ binding at the transport site. The drawbacks of models in which Mn2+ stimulates pNPPase by binding solely to the catalytic site vs. those in which Mn2+ stimulates by binding to both the catalytic and transport sites are presented. Our results provide new insights into the
pNPPase kinetic mechanism as well as how divalent cations interact with the Na pump. 相似文献
13.
Tissue-distinct interactions of theNa+-K+-ATPasewith Na+ andK+, independent ofisoform-specific properties, were reported previously (A. G. Therien,N. B. Nestor, W. J. Ball, and R. Blostein. J. Biol.Chem. 271: 7104-7112, 1996). In this paper, wedescribe a detailed analysis of tissue-specific kinetics particularlyrelevant to regulation of pump activity by intracellularK+, namelyK+ inhibition at cytoplasmicNa+ sites. Our results show thatthe order of susceptibilities of 1 pumps of various rat tissuestoK+/Na+antagonism, represented by the ratio of the apparent affinity forNa+ binding at cytoplasmicactivation sites in the absence ofK+ to the affinity constant forK+ as a competitive inhibitor ofNa+ binding at cytoplasmic sites,is red blood cell < axolemma rat1-transfected HeLa cells < small intestine < kidney < heart. In addition, we havecarried out an extensive analysis of the kinetics ofK+ binding and occlusion to thecytoplasmic cation binding site and find that, for most tissues, thereis a relationship between the rate ofK+ binding/occlusion and theapparent affinity for K+ as acompetitive inhibitor of Na+activation, the order for both parameters being heart kidney > small intestine rat1-transfected HeLa cells. Thenotion that modulations in cytoplasmicK+/Na+antagonism are a potential mode of pump regulation is underscored byevidence of its reversibility. Thus the relatively highK+/Na+antagonism characteristic of kidney pumps was reduced when rat kidneymicrosomal membranes were fused into the dog red blood cell. 相似文献
14.
Role of Na+/Ca2+ exchange in regulating cytosolic Ca2+ in cultured human pulmonary artery smooth muscle cells 总被引:3,自引:0,他引:3
Zhang S Yuan JX Barrett KE Dong H 《American journal of physiology. Cell physiology》2005,288(2):C245-C252
A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) in pulmonary artery smooth muscle cells (PASMC) is an important stimulus for cell contraction, migration, and proliferation. Depletion of intracellular Ca2+ stores opens store-operated Ca2+ channels (SOC) and causes Ca2+ entry. Transient receptor potential (TRP) cation channels that are permeable to Na+ and Ca2+ are believed to form functional SOC. Because sarcolemmal Na+/Ca2+ exchanger has also been implicated in regulating [Ca2+]cyt, this study was designed to test the hypothesis that the Na+/Ca2+ exchanger (NCX) in cultured human PASMC is functionally involved in regulating [Ca2+]cyt by contributing to store depletion-mediated Ca2+ entry. RT-PCR and Western blot analyses revealed mRNA and protein expression for NCX1 and NCKX3 in cultured human PASMC. Removal of extracellular Na+, which switches the Na+/Ca2+ exchanger from the forward (Ca2+ exit) to reverse (Ca2+ entry) mode, significantly increased [Ca2+]cyt, whereas inhibition of the Na+/Ca2+ exchanger with KB-R7943 (10 µM) markedly attenuated the increase in [Ca2+]cyt via the reverse mode of Na+/Ca2+ exchange. Store depletion also induced a rise in [Ca2+]cyt via the reverse mode of Na+/Ca2+ exchange. Removal of extracellular Na+ or inhibition of the Na+/Ca2+ exchanger with KB-R7943 attenuated the store depletion-mediated Ca2+ entry. Furthermore, treatment of human PASMC with KB-R7943 also inhibited cell proliferation in the presence of serum and growth factors. These results suggest that NCX is functionally expressed in cultured human PASMC, that Ca2+ entry via the reverse mode of Na+/Ca2+ exchange contributes to store depletion-mediated increase in [Ca2+]cyt, and that blockade of the Na+/Ca2+ exchanger in its reverse mode may serve as a potential therapeutic approach for treatment of pulmonary hypertension. sodium-calcium exchange; calcium homeostasis; vascular smooth muscle 相似文献
15.
Foroutan S Brillault J Forbush B O'Donnell ME 《American journal of physiology. Cell physiology》2005,289(6):C1492-C1501
Brain edema that forms during the early stages of stroke involves increased transport of Na+ and Cl across an intact blood-brain barrier (BBB). Our previous studies have shown that a luminal BBB Na+-K+-Cl cotransporter is stimulated by conditions present during ischemia and that inhibition of the cotransporter by intravenous bumetanide greatly reduces edema formation in the rat middle cerebral artery occlusion model of stroke. The present study focused on investigating the effects of hypoxia, which develops rapidly in the brain during ischemia, on the activity and expression of the BBB Na+-K+-Cl cotransporter, as well as on Na+-K+-ATPase activity, cell ATP content, and intracellular volume. Cerebral microvascular endothelial cells (CMECs) were assessed for Na+-K+-Cl cotransporter and Na+-K+-ATPase activities as bumetanide-sensitive and ouabain-sensitive 86Rb influxes, respectively. ATP content was assessed by luciferase assay and intracellular volume by [3H]-3-O-methyl-D-glucose and [14C]-sucrose equilibration. We found that 30-min exposure of CMECs to hypoxia ranging from 7.5% to 0.5% O2 (vs. 19% normoxic O2) significantly increased cotransporter activity as did 7.5% or 2% O2 for up to 2 h. This was not associated with reduction in Na+-K+-ATPase activity or ATP content. CMEC intracellular volume increased only after 4 to 5 h of hypoxia. Furthermore, glucose and pyruvate deprivation increased cotransporter activity under both normoxic and hypoxic conditions. Finally, we found that hypoxia increased phosphorylation but not abundance of the cotransporter protein. These findings support the hypothesis that hypoxia stimulation of the BBB Na+-K+-Cl cotransporter contributes to ischemia-induced brain edema formation. edema; blood-brain barrier; bumetanide; cell volume 相似文献
16.
Apoptosis repressor with caspase domain inhibits cardiomyocyte apoptosis by reducing K+ currents 总被引:8,自引:0,他引:8
Ekhterae D Platoshyn O Zhang S Remillard CV Yuan JX 《American journal of physiology. Cell physiology》2003,284(6):C1405-C1410
Cell shrinkageis an early prerequisite in programmed cell death, and cytoplasmicK+ is a dominant cation that controls intracellular ionhomeostasis and cell volume. Blockade of K+ channelsinhibits apoptotic cell shrinkage and attenuates apoptosis. We examined whether apoptotic repressor with caspase recruitment domain (ARC), an antiapoptotic protein, inhibits cardiomyocyte apoptosis by reducing K+ efflux throughvoltage-gated K+ (Kv) channels. In heart-derived H9c2cells, whole cell Kv currents (IK(V)) wereisolated by using Ca2+-free extracellular (bath) solutionand including 5 mM ATP and 10 mM EGTA in the intracellular (pipette)solution. Extracellular application of 5 mM 4-aminopyridine (4-AP), ablocker of Kv channels, reversibly reduced IK(V)by 50-60% in H9c2 cells. The remaining currents during 4-APtreatment may be generated by K+ efflux through4-AP-insensitive K+ channels. Overexpression of ARC inheart-derived H9c2 cells significantly decreasedIK(V), whereas treatment with staurosporine, apotent apoptosis inducer, enhanced IK(V)in wild-type cells. The staurosporine-induced increase inIK(V) was significantly suppressed and thestaurosporine-mediated apoptosis was markedly inhibited incells overexpressing ARC compared with cells transfected with thecontrol neomycin vector. These results suggest that theantiapoptotic effect of ARC is, in part, due to inhibition of Kvchannels in cardiomyocytes. 相似文献
17.
Cougnon Marc; Bouyer Patrice; Jaisser Frederic; Edelman Aleksander; Planelles Gabrielle 《American journal of physiology. Cell physiology》1999,277(2):C280
Functional expression of the rat colonicH+-K+-ATPasewas obtained by coexpressing its catalytic -subunit and the1-subunit of theNa+-K+-ATPasein Xenopus laevis oocytes. We observedthat, in oocytes expressing the rat colonicH+-K+-ATPasebut not in control oocytes (expressing1 alone),NH4Cl induced a decrease in86Rb uptake and the initial rateof intracellular acidification induced by extracellularNH4Cl was enhanced, consistentwith NH+4 influx via the colonicH+-K+-ATPase.In the absence of extracellularK+, only oocytes expressing thecolonicH+-K+-ATPasewere able to acidify an extracellular medium supplemented withNH4Cl. In the absence ofextracellular K+ and in thepresence of extracellular NH+4, intracellular Na+ activity in oocytes expressingthe colonicH+-K+-ATPasewas lower than that in control oocytes. A kinetic analysis of86Rb uptake suggests thatNH+4 acts as a competitive inhibitor of thepump. Taken together, these results are consistent withNH+4 competition forK+ on the external site of thecolonicH+-K+-ATPaseand with NH+4 transport mediated by this pump. 相似文献
18.
This paper reports the effects of low O2 concentration (001,0055, and 0.115mol m3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (02mm) than in the expanding tissues (24 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (412 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (02mm) K + /Na+ selectivity was already reduced at 0.115 mol m3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues 相似文献
19.
Murata Yoshiyuki; Yoshihashi Manabu; Obi Ichiro; Kakutani Tadaaki 《Plant & cell physiology》1998,39(10):1039-1044
The patch-clamp technique was used to study effect of the Ca2+on K+ channels in the plasma membrane of protoplasts isolatedfrom tobacco (Nicotiana tabacum L., cv. Bright Yellow) culturedcells in suspension. The outward rectifying whole-cell K+ currentswere not affected by in-tracellular Ca2+, but they were reducedwith increasing extracellular Ca2+. Neither extracellular norintracellular Ca2+ affected the permeability ratios (pK+/PNa+)of the plasma membrane. These results suggest that the inhibitionof outward-rectifying K+ channels by extracellular Ca2+may partiallycontribute towards the mitigation of detrimental effects ofsalinity on growth by extracellular Ca2+. (Received January 19, 1998; Accepted July 30, 1998) 相似文献
20.
A guinea pig kidney membrane preparation was incubated with thimerosal and then thoroughly washed. Comparison of the properties of the native and the modified membranes showed that (a) Na++K+-dependent activity is substantially inhibited by thimerosal; (b) thimerosal does not diminish Na+-dependent ATPase activity; and (c) the thimerosal treated enzyme, like the native enzyme, is phosphorylated in the presence of Na+ and ATP, and dephosphorylated upon the addition of K+. It is suggested that thimerosal does not affect the binding of ATP to the high-affinity catalytic site, but that it blocks the binding of ATP to a low affinity modifying site the occupation of which is essential for the dissociation of the stable K+-dephosphoenzyme and the recycling of the enzyme. 相似文献