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1.
In single water-sensitive fibers (water fibers) of the frogglossopharyngeal nerve, application of a solution of 500 mMcholine Cl to the tongue elicited responses of varying magnitude.Some water fibers (plain choline-insensitive water fibers) barelyresponded to the solution, while some water fibers (plain choline-sensitivewater fibers) exhibited a considerable response to this solution.NiCl2. which is barely effective in producing neural responseat concentrations below 5 mM, induced the response of plaincholine-insensitrve water fibers to choline+ ions. It was confirmed,in a collision test, that the Ni2+-induced responses to choline+ions were derived from water fibers. However, NiCl2 did notaffect the magnitude of me response generated by choline+ ionsin plain choline-sensitive water fibers. The concentration-responsecurve for choline Cl in the presence of 1 mM NiCl2 for plaincholine-insensitive water fibers was similar to the curves obtainedin the absence of NiCl2 for plain choline-sensitive water fibers.Other organic salts, such as tris(hydroxymethyl)arrdnomethane-HCl,triethanotamine-HCl and tetraethylammonium Cl, elicited no responseor only a very small response from water fibers, and NiCl2 didnot affect these responses. It is suggested that there existsa choline receptor for the response to choline+ ions in theapical membrane of frog taste cells and that Ni2+ ions exposethe sites of such choline receptors, which are deeply embeddedin the receptor membrane, to the outside medium. The effectof Ni2+ ions results in an increase in the number of the cholinereceptor sites available for binding of choline+ ions. The rankorder of effectiveness of transition metal ions in elicitingthe appearance or enhancement of the response to choline Clwas Ni2+ > Co2+ > Mn2+. Mg2+ ions had no effect on theresponse to choline+ ions. A similar rank order was previouslyobtained in enhancement of the responses to Ca2+, Mg2+ and Na2+ions (Kitada, 1994a). It seems likely that the mechanism forenhancement or elicitation of the response to choline+ ionsby the transition metal ions has features in common with thatfor enhancement of the responses to Ca2+, Mg2+ and Na+ ions. 相似文献
2.
Unitary discharges from single water fibers of the frog glossopharyngealnerve, caused by stimulation with 0.025 mM CaSO4, wererecorded from fungiform papillae with a suction electrode. NiSO4at concentrations of 0.22 mM, namely, at concentrationsthat are barely effective in producing impulses, had a dualaction on the Ca2+ response: NiSO4 caused both inhibition andenhancement of the Ca2+ response. In the present study, thisdual action of Ni2+ ions on the Ca2+ response was investigatedin detail. Single water fibers yielded a saturation type ofconcentration-response curve for CaSO4, which suggested thatsulfateions do not affect the Ca2+ response. Thus, sulfateswere used as test salts in the present study. At low concentrationsof Ca2+ ions, Ni2+ ions inhibited the Ca2+ response, but athigher concentrations of Co2+ ions they enhanced it. The resultscan be explained quantitatively by the hypothesis that Ni2+ions inhibit the Ca2+ response by competing with Ca2+ ions forthe Ca2+ receptor (Xca) that is responsible for the Ca2+ responseand that Ni2+ ions enhance the Ca2+ response by acting on amembrane element that interacts with Xca. Double-reciprocalplots of the data indicate that the enhancing action of Ni2+ions is saturated at 12 mM Ni2+ ions and that Ni2+ ionsat these concentrations increase the maximal response of theCa2+ response by 182%. Dissociation constants for the Ca-Xcacomplex and the Ni-Xca, complex were 4.2 x 105 M and7.6 x 105 M, respectively. The analysis suggests thatNi2+ ions enhance the Ca2+ response by affecting the Ca-Xcacomplex without altering the affinity of Xca, for Ca2+ ions. 相似文献
3.
Single water fibers of the frog glossopharyngeal nerve respondto relatively high concentrations of NaCl (>80 mM). NiCl2at 1 mM enhanced the Na+ response and reduced the thresholdconcentration for NaCl to 20 mM. CaCl2 at 0.51 mM inducedan inhibition of the Ni2+-enhanced response to Na+ ions. A quantitativeexplanations for these results is provided by the hypothesisthat Ni2+ ions secondarily affect a sodium receptor or channel(designated XNa*) that is responsible for the Na+ response andthat Ca2+ ions inhibit the Ni2+-enhanced response to Na+ ionsby competing with Na+ ions for XNa*. Double-reciprocal plotsof the experimental data indicate that the affinity of XNa*for both Na+ ions (agonist) and Ca2+ ions (competitive antagonist)in the presence of 1 mM NiCl2 was five times higher than thepreviously reported values obtained in the absence of NiCl2(Kitada, 1991). Ni2+ ions at 1 mM enhanced the maximal responseto Na+ ions by 190%. It appears that a sodium receptor (or channel)interacts with a Ni2+-binding element that is affected by Ni2+ions and, thus, Ni2+ ions can induce both an increase in theaffinity of the sodium receptor for the respective cations andan enhancement of the Na+ response. Chem Senses 21: 6573,1996. 相似文献
4.
Fibers of the frog glossopharyngeal nerve (water fibers) thatare sensitive to water also respond to CaCl2, MgCl2 and NaCl.In the present study, interaction among cations (Ca2+, Mg2+and Na+) on taste cell membrane in frogs was studied using transitionmetals (NiCl2, CoCl2 and MnCl2), which themselves are barelyeffective in producing neural response at concentrations below5 mM. Unitary discharges from single water fibers were recordedfrom fungiform papillae with suction electrode. Transition metalions (0.055.0 mM) had exclusively enhancing effects onthe responses to 50 mM Ca2+, 100 mM Mg2+ and 500 mM Na+. Theeffects of transition metal ions were always reversible. Therank order of effectiveness of transition metals at 1 mM inthe enhancement of the responses to 50 mM CaCl2, 100 mM MgCl2and 500 mM NaCl was NiCl2 > CoCl2 > MnCl2. The concentrationof transition metal ions effective to enhance salt responsewas almost the same among Ca2+, Mg2+ and Na+ responses. Theresults suggest that a common mechanism is involved in the enhancementof Ca2+, Mg2+ and Na+ taste responses. The enhanced Mg2+ responseand the enhanced Na+ response were greatly inhibited by theaddition of Ca2+ ions, and the enhanced Ca2+ response was inhibitedby the addition of Mg2+ or Na+ ions, suggesting that competitiveantagonism occurs between Ca2+ and Mg2+ ions and between Ca2+and Na+ ions in the presence of Ni2+ ions. Ni2+ ions had a dualeffect on the Ca2+ response induced by low concentration (0.1mM) of CaCl2: enhancement at lower concentrations (0.020.1mM) of NiCl2 and inhibition at higher concentrations (0.55mM)of NiCl2. The present results suggest that transition metalions do not affect the receptor-antagonist complex, but affectonly the receptor-agonist complex. 相似文献
5.
In the frog glossopharyngeal nerve, single water fibers respondto low CaCl2 (12 mM) and relatively high MgCl2 (100 mM).In the present study, it was found that stimulation by a mixtureof low CaCl2 and relatively high MgCl2 led to a small response.This suggests that the Ca+ response is inhibited by the presenceof Mg2+ and the Mg2+ response is inhibited by the presence ofCa2+. Hence, it is suggested that there are different receptorsites for divalent cations in single water fibers of the frogglossopharyngeal nerve, a calcium receptor site (XCa) responsiblefor the Ca2+ response and a magnesium receptor site (XMg) responsiblefor the Mg2+ response. It has been reported that Mg2+ inhibitsthe Ca2+ response by competing with Ca2+ for XCa (Kitada andShimada, 1980). In the present study, the inhibition of theMg2+ response by Ca2+ was examined quantitatively under theassumption that the magnitude of the neural response is proportionalto the amount of MgXMg complex minus a constant (the thresholdconcentration of the MgXMg complex). The results obtained indicatethat Ca2+ competes with Mg2+ for XMg. The apparent dissociationconstants for MgXMg complex and CaXMg complex, which were obtainedfrom the present study, were 8.0 x 102 M and 7.2 x 104M, respectively. Thus, competition between Ca+ and Mg2+ forthe distinct receptor sites involved in taste reception wasdemonstrated by the results described in this paper. Since thedivalent cations do not always bring about activation of tastereceptors, the responses to salts in the frog glossopharyngealnerve cannot be explained in terms of changes in the surfacepotential outside the taste cells. The present results suggestthat there exist multiple specific receptor sites for cationsinvolved in salt taste responses, and only the binding of eachseparate cation to its appropriate receptor sites leads to activationof the receptor and the initiation of impulses in sensory nerveendings. 相似文献
6.
Single fibers of the frog glossopharyngeal nerve respond toMgCl2 at concentrations exceeding 10 mM. NiCl2 at 1 mM enhancedthe Mg2+ response. CaCl2 at 0.52 mM induced an inhibitionof the Ni2+-enhanced response to Mg2+ ions. A quantitative explanationfor these results is provided by the hypothesis that Ni2+ ionssecondarily affect a magnesium receptor (designated X*Mg) thatis responsible for the Mg2+ response and that Ca2+ ions inhibitthe Ni2+-enhanced response to Mg2+ ions by competing with Mg2+ions for X*Mg. Double-reciprocal plots of the experimental dataindicate that Ni2+ ions do not affect the affinities of X*Mgfor both Mg2+ ions (agonist) and Ca2+ ions (competitive antagonist)appreciably, and that Ni2+ ions at 1 mM enhanced the maximalresponse to Mg2+ ions by 270%. It appears that a magnesium receptorinteracts with an Ni2+-binding element that is affected by Ni2+ions and, thus, Ni2+ ions can induce an enhancement of the Mg2+response. Chem. Senses 22: 613622,1997. 相似文献
7.
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
8.
In fura 2-loaded N1E-115 cells, regulationof intracellular Ca2+ concentration([Ca2+]i) following a Ca2+ loadinduced by 1 µM thapsigargin and 10 µM carbonylcyanidep-trifluoromethyoxyphenylhydrazone (FCCP) wasNa+ dependent and inhibited by 5 mM Ni2+. Incells with normal intracellular Na+ concentration([Na+]i), removal of bath Na+,which should result in reversal of Na+/Ca2+exchange, did not increase [Ca2+]i unlesscell Ca2+ buffer capacity was reduced. When N1E-115 cellswere Na+ loaded using 100 µM veratridine and 4 µg/mlscorpion venom, the rate of the reverse mode of theNa+/Ca2+ exchanger was apparently enhanced,since an ~4- to 6-fold increase in [Ca2+]ioccurred despite normal cell Ca2+ buffering. In SBFI-loadedcells, we were able to demonstrate forward operation of theNa+/Ca2+ exchanger (net efflux ofCa2+) by observing increases (~ 6 mM) in[Na+]i. These Ni2+ (5 mM)-inhibited increases in [Na+]i could onlybe observed when a continuous ionomycin-induced influx ofCa2+ occurred. The voltage-sensitive dyebis-(1,3-diethylthiobarbituric acid) trimethine oxonol was used tomeasure changes in membrane potential. Ionomycin (1 µM) depolarizedN1E-115 cells (~25 mV). This depolarization was Na+dependent and blocked by 5 mM Ni2+ and 250-500 µMbenzamil. These data provide evidence for the presence of anelectrogenic Na+/Ca2+ exchanger that is capableof regulating [Ca2+]i after release ofCa2+ from cell stores. 相似文献
9.
Vela J Pérez-Millán MI Becu-Villalobos D Díaz-Torga G 《American journal of physiology. Cell physiology》2007,293(3):C951-C959
The L-type Ca2+ channel is the primary voltage-dependent Ca2+-influx pathway in many excitable and secretory cells, and direct phosphorylation by different kinases is one of the mechanisms involved in the regulation of its activity. The aim of this study was to evaluate the participation of Ser/Thr kinases and tyrosine kinases (TKs) in depolarization-induced Ca2+ influx in the endocrine somatomammotrope cell line GH3. Intracellular Ca2+ concentration ([Ca2+]i) was measured using a spectrofluorometric method with fura 2-AM, and 12.5 mM KCl (K+) was used as a depolarization stimulus. K+ induced an abrupt spike (peak) in [Ca2+]i that was abolished in the presence of nifedipine, showing that K+ enhances [Ca2+]i, preferably activating L-type Ca2+ channels. H89, a selective PKA inhibitor, significantly reduced depolarization-induced Ca2+ mobilization in a concentration-related manner when it was applied before or after K+, and okadaic acid, an inhibitor of Ser/Thr phosphatases, which has been shown to regulate PKA-stimulated L-type Ca2+ channels, increased K+-induced Ca2+ entry. When PKC was activated by PMA, the K+-evoked peak in [Ca2+]i, as well as the plateau phase, was significantly reduced, and chelerythrine (a PKC inhibitor) potentiated the K+-induced increase in [Ca2+]i, indicating an inhibitory role of PKC in voltage-dependent Ca2+ channel (VDCC) activity. Genistein, a TK inhibitor, reduced the K+-evoked increase in [Ca2+]i, but, unexpectedly, the tyrosine phosphatase inhibitor orthovanadate reduced not only basal Ca2+ levels but, also, Ca2+ influx during the plateau phase. Both results suggest that different TKs may act differentially on VDCC activation. Activation of receptor TKs with epidermal growth factor (EGF) or vascular endothelial growth factor potentiated K+-induced Ca2+ influx, and AG-1478 (an EGF receptor inhibitor) decreased it. However, inhibition of the non-receptor TK pp60 c-Src enhanced K+-induced Ca2+ influx. The present study strongly demonstrates that a complex equilibrium among different kinases and phosphatases regulates VDCC activity in the pituitary cell line GH3: PKA and receptor TKs, such as vascular endothelial growth factor receptor and EGF receptor, enhance depolarization-induced Ca2+ influx, whereas PKC and c-Src have an inhibitory effect. These kinases modulate membrane depolarization and may therefore participate in the regulation of a plethora of intracellular processes, such as hormone secretion, gene expression, protein synthesis, and cell proliferation, in pituitary cells. phosphatases; protein kinase A; protein kinase C; epidermal growth factor 相似文献
10.
Coupling of L-type voltage-sensitive calcium channels to P2X(2) purinoceptors in PC-12 cells 总被引:1,自引:0,他引:1
Extracellular ATPelevates cytosolic Ca2+ by activating P2X and P2Ypurinoceptors and voltage-sensitive Ca2+ channels (VCCCs)in PC-12 cells, thereby facilitating catecholamine secretion. Weinvestigated the mechanism by which ATP activates VSCCs.2-Methylthioadenosine 5'-triphosphate (2-MeS-ATP) and UTP were used aspreferential activators of P2X and P2Y, respectively. Nifedipineinhibited the ATP- and 2-MeS-ATP-evoked cytosolic Ca2+concentration increase and [3H]norepinephrine secretion,but not the UTP-evoked responses. Studies with Ca2+ channelblockers indicated that L-type VSCCs were activated after the P2Xactivation. Mn2+ entry profiles and studies withthapsigargin revealed that Ca2+ entry, rather thanCa2+ release, was sensitive to nifedipine. AlthoughP2X2 and P2X4 receptor mRNAs were detected,studies with pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acidrevealed that P2X2 was mainly coupled to the L-type VSCCs. The inhibitory effect of nifedipine did not occur in the absence ofextracellular Na+, suggesting that Na+ influx,which induces depolarization, was essential for theP2X2-mediated activation of VSCCs. We report thatdepolarization induced by Na+ entry through theP2X2 purinoceptors effectively activates L-type VSCCs inPC-12 cells. 相似文献
11.
Xu W Wilson BJ Huang L Parkinson EL Hill BJ Milanick MA 《American journal of physiology. Cell physiology》2000,278(5):C965-C972
Theplasma membrane Ca2+ pump is known to mediateCa2+/H+ exchange. Extracellular protonsactivated 45Ca2+ efflux from human red bloodcells with a half-maximal inhibition constant of 2 nM when theintracellular pH was fixed. An increase in pH from 7.2 to 8.2 decreasedthe IC50 for extracellular Ca2+ from ~33 to~6 mM. Changing the membrane potential by >54 mV had no effect onthe IC50 for extracellular Ca2+. This arguesagainst Ca2+ release through a high-field access channel.Extracellular Ni2+ inhibited Ca2+ efflux withan IC50 of 11 mM. Extracellular Cd2+ inhibitedwith an IC50 of 1.5 mM, >10 times better thanCa2+. The Cd2+ IC50 also decreasedwhen the pH was raised from 7.1 to 8.2, consistent withCa2+, Cd2+, and H+ competing forthe same site. The higher affinity for inhibition by Ni2+and Cd2+ is consistent with a histidine or cysteine as partof the release site. The cysteine reagent 2-(trimethylammonium)ethylmethanethiosulfonate did not inhibit Ca2+ efflux. Ourresults are consistent with the notion that the release site contains a histidine. 相似文献
12.
Evidence for Na+/Ca2+ exchange in intact single skeletal muscle fibers from the mouse 总被引:1,自引:0,他引:1
Balnave Christopher D.; Allen David G. 《American journal of physiology. Cell physiology》1998,274(4):C940
The myoplasmic free Ca2+concentration([Ca2+]i)was measured in intact single fibers from mouse skeletal muscle withthe fluorescent Ca2+ indicatorindo 1. Some fibers were perfused in a solution in which theconcentration of Na+ was reducedfrom 145.4 to 0.4 mM (low-Na+solution) in an attempt to activate reverse-modeNa+/Ca2+exchange (Ca2+ entry in exchangefor Na+ leaving the cell). Undernormal resting conditions, application oflow-Na+ solution only increased[Ca2+]iby 5.8 ± 1.8 nM from a mean resting[Ca2+]iof 42 nM. In other fibers,[Ca2+]iwas elevated by stimulating sarcoplasmic reticulum (SR)Ca2+ release with caffeine (10 mM)and by inhibiting SR Ca2+ uptakewith2,5-di(tert-butyl)-1,4-benzohydroquinone(TBQ; 0.5 µM) in an attempt to activate forward-modeNa+/Ca2+exchange (Ca2+ removal from thecell in exchange for Na+ influx).These two agents caused a large increase in[Ca2+]i,which then declined to a plateau level approximately twice the baseline[Ca2+]iover 20 min. If the cell was allowed to recover between exposures tocaffeine and TBQ in a solution in whichCa2+ had been removed, theincrease in[Ca2+]iduring the second exposure was very low, suggesting thatCa2+ had left the cell during theinitial exposure. Application of caffeine and TBQ to a preparation inlow-Na+ solution produced a large,sustained increase in[Ca2+]iof ~1 µM. However, when cells were exposed to caffeine and TBQ in alow-Na+ solution in whichCa2+ had been removed, a sustainedincrease in[Ca2+]iwas not observed, although[Ca2+]iremained higher and declined slower than in normalNa+ solution. This suggests thatforward-modeNa+/Ca2+exchange contributed to the fall of[Ca2+]iin normal Na+ solution, but whenextracellular Na+ was low, aprolonged elevation of[Ca2+]icould activate reverse-modeNa+/Ca2+exchange. The results provide evidence that skeletal muscle fibers possess aNa+/Ca2+exchange mechanism that becomes active in its forward mode when [Ca2+]iis increased to levels similar to that obtained during contraction. 相似文献
13.
Nakamura Yoshiyuki; Kasamo Kunihiro; Sakata Makato; Ohta Eiji 《Plant & cell physiology》1992,33(2):139-149
Extrusion of protons as a response to high-NaCl stress in intactmung bean roots was investigated at different external concentrationsof Ca2+ ions ([Ca2+]ex). The extrusion of protons was graduallyenhanced in the roots exposed to 100 mM NaCl, and high [Ca2+]exdiminished this enhancement of the extrusion. Vesicles of plasmalemmaand tonoplast were prepared from the roots and the H+-translocatingATPase (H+-ATPase) activities associated with the two typesof membrane and the H+-pyrophosphatase (H+-PPase) activity ofthe tonoplast were assayed. The plasmalemma ATPase was stimulatedin parallel with dramatic increases in the intracellular concentrationof Na+([Na+]in). High [Ca2+]ex prevented the increase in [Na+]inand diminished the stimulation of ATPase activity. The tonoplastATPase showed a rapid response to salt stress and was similarlystimulated even at high [Ca2+]M. The activities of both ATPaseswere, however, insensitive to concentrations of Na+ ions upto 100 HIM. By contrast, H+-PPase activity of the tonoplastwas severely inhibited with increasing [Na+]in under salt stressand recovered with high [Ca2+]ex. These findings suggest thathigh-NaCl stress increases the intracellular concentration ofNa+ ions in mung bean roots, which inhibits the tonoplast H+-PPase,and the activity of the plasmalemma H+-ATPase is thereby stimulatedand regulates the cytoplasmic pH. (Received March 26, 1991; Accepted December 13, 1991) 相似文献
14.
Adenosine stimulates depolarization and rise in cytoplasmic [Ca2+] in type I cells of rat carotid bodies 总被引:1,自引:0,他引:1
During hypoxia, the level of adenosine in the carotid bodies increases as a result of ATP catabolism and adenosine efflux via adenosine transporters. Using Ca2+ imaging, we found that adenosine, acting via A2A receptors, triggered a rise in cytoplasmic [Ca2+] ([Ca2+]i) in type I (glomus) cells of rat carotid bodies. The adenosine response could be mimicked by forskolin (but not its inactive analog), and could be abolished by the PKA inhibitor H89. Simultaneous measurements of membrane potential (perforated patch recording) and [Ca2+]i showed that the adenosine-mediated [Ca2+]i rise was accompanied by depolarization. Ni2+, a voltage-gated Ca2+ channel (VGCC) blocker, abolished the adenosine-mediated [Ca2+]i rise. Although adenosine was reported to inhibit a 4-aminopyridine (4-AP)-sensitive K+ current, 4-AP failed to trigger any [Ca2+]i rise, or to attenuate the adenosine response. In contrast, anandamide, an inhibitor of the TWIK-related acid-sensitive K+-1 (TASK-1) channels, triggered depolarization and [Ca2+]i rise. The adenosine response was attenuated by anandamide but not by tetraethylammonium. Our results suggest that adenosine, acting via the adenylate cyclase and PKA pathways, inhibits the TASK-1 K+ channels. This leads to depolarization and activation of Ca2+ entry via VGCC. This excitatory action of adenosine on type I cells may contribute to the chemosensitivity of the carotid body during hypoxia. O2 sensing; A2A receptor; cAMP; protein kinase A; TWIK-related acid-sensitive K+ channel 相似文献
15.
The effects of Pi onsarcoplasmic reticulum (SR) Ca2+ regulation were studied inmechanically skinned rat skeletal muscle fibers. Brief application ofcaffeine was used to assess the SR Ca2+ content, andchanges in concentration of Ca2+([Ca2+]) within the cytosol were detected withfura 2 fluorescence. Introduction of Pi (1-40 mM)induced a concentration-dependent Ca2+ efflux from the SR.In solutions lacking creatine phosphate (CP), the amplitude of thePi-induced Ca2+ transient approximatelydoubled. A similar potentiation of Pi-induced Ca2+ release occurred after inhibition of creatine kinase(CK) with 2,4-dinitrofluorobenzene. In the presence of ruthenium red or ryanodine, caffeine-induced Ca2+ release was almostabolished, whereas Pi-induced Ca2+ release wasunaffected. However, introduction of the SR Ca2+ ATPaseinhibitor cyclopiazonic acid effectively abolishedPi-induced Ca2+ release. These data suggestthat Pi induces Ca2+ release from the SR byreversal of the SR Ca2+ pump but not via the SRCa2+ channel under these conditions. If this occurs inintact skeletal muscle during fatigue, activation of a Ca2+efflux pathway by Pi may contribute to the reporteddecrease in net Ca2+ uptake and increase in resting[Ca2+]. 相似文献
16.
With slight modifications, conventional assay procedures forK+, Na+, Ca2+, Mg2+, Cl, NO3, H2PO4, fructoseand fructose-yielding saccharides, and glucose were applicableto the extract of Phaseolus pulvini. About 10 ml of a hot-waterextract from about 30 mg fresh weight of the pulvini was sufficientfor separate measurement of the ions and saccharides named above. (Received August 7, 1979; ) 相似文献
17.
Micci M. A.; Christensen Burgess N. 《American journal of physiology. Cell physiology》1998,274(6):C1625
The role of theNa+/Ca2+exchanger in intracellular Ca2+regulation was investigated in freshly dissociated catfish retinalhorizontal cells (HC).Ca2+-permeable glutamate receptorsand L-type Ca2+ channels as wellas inositol 1,4,5-trisphosphate-sensitive and caffeine-sensitiveintracellular Ca2+ stores regulateintracellular Ca2+ in these cells.We used the Ca2+-sensitive dyefluo 3 to measure changes in intracellularCa2+ concentration([Ca2+]i)under conditions in whichNa+/Ca2+exchange was altered. In addition, the role of theNa+/Ca2+exchanger in the refilling of the caffeine-sensitiveCa2+ store followingcaffeine-stimulated Ca2+ releasewas assessed. Brief applications of caffeine (1-10 s) producedrapid and transient changes in[Ca2+]i.Repeated applications of caffeine produced smallerCa2+ transients until no furtherCa2+ was released. Store refillingoccurred within 1-2 min and required extracellularCa2+. Ouabain-induced increases inintracellular Na+ concentration([Na+]i)increased both basal free[Ca2+]iand caffeine-stimulated Ca2+release. Reduction of external Na+concentration([Na+]o)further and reversibly increased[Ca2+]iin ouabain-treated HC. This effect was not abolished by the Ca2+ channel blocker nifedipine,suggesting that increases in[Na+]ipromote net extracellular Ca2+influx through aNa+/Ca2+exchanger. Moreover, when[Na+]owas replaced by Li+, caffeine didnot stimulate release of Ca2+ fromthe caffeine-sensitive store afterCa2+ depletion. TheNa+/Ca2+exchanger inhibitor 2',4'-dimethylbenzamil significantlyreduced the caffeine-evoked Ca2+response 1 and 2 min after store depletion. 相似文献
18.
Naro F De Arcangelis V Coletti D Molinaro M Zani B Vassanelli S Reggiani C Teti A Adamo S 《American journal of physiology. Cell physiology》2003,284(4):C969-C976
Cytoplasmic Ca2+concentration ([Ca2+]i) variation is akey event in myoblast differentiation, but the mechanism by which itoccurs is still debated. Here we show that increases of extracellular Ca2+ concentration ([Ca2+]o)produced membrane hyperpolarization and a concentration-dependent increase of [Ca2+]i due to Ca2+influx across the plasma membrane. Responses were not related toinositol phosphate turnover and Ca2+-sensing receptor.[Ca2+]o-induced[Ca2+]i increase was inhibited byCa2+ channel inhibitors and appeared to be modulated byseveral kinase activities. [Ca2+]i increasewas potentiated by depletion of intracellular Ca2+ storesand depressed by inactivation of the Na+/Ca2+exchanger. The response to arginine vasopressin (AVP), which inducesinositol 1,4,5-trisphosphate-dependent[Ca2+]i increase in L6-C5 cells, was notmodified by high [Ca2+]o. On the contrary,AVP potentiated the [Ca2+]i increase in thepresence of elevated [Ca2+]o. Other clones ofthe L6 line as well as the rhabdomyosarcoma RD cell line and thesatellite cell-derived C2-C12 line expressed similar responses to high[Ca2+]o, and the amplitude of the responseswas correlated with the myogenic potential of the cells. 相似文献
19.
DiPolo R Berberián G Beaugé L 《American journal of physiology. Cell physiology》2000,279(5):C1631-C1639
We investigated the role of intracellular Mg2+(Mgi2+) on the ATP regulation ofNa+/Ca2+ exchanger in squid axons and bovineheart. In squid axons and nerve vesicles, the ATP-upregulated exchangerremains activated after removal of cytoplasmic Mg2+, evenin the absence of ATP. Rapid and complete deactivation of theATP-stimulated exchange occurs upon readmission ofMgi2+. At constant ATP concentration, the effectof intracellular Mg2+ concentration([Mg2+]i) on the ATP regulation of exchangeris biphasic: activation at low [Mg2+]i,followed by deactivation as [Mg2+]i isincreased. No correlation was found between the above results and thelevels of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] measured innerve membrane vesicles. Incorporation ofPtdIns(4,5)P2 into membrane vesicles activates Na+/Ca2+ exchange in mammalian heart but not insquid nerve. Moreover, an exogenous phosphatase prevents MgATPactivation in squid nerves but not in mammalian heart. It is concludedthat 1) Mgi2+ is an essentialcofactor for the deactivation part of ATP regulation of the exchangerand 2) the metabolic pathway of ATP upregulation of theNa+/Ca2+ exchanger is different in mammalianheart and squid nerves. 相似文献
20.
Ion Composition of the Chara Internode 总被引:2,自引:0,他引:2
Ion compositions of the cytoplasm and the vacuole of Chara australiswere analyzed according to Kishimoto and Tazawa (1964) and Kiyosawa(1979a). The ions in the cytoplasm and the vacuole analyzedwere K+, Na+, Ca2+, Mg2+, Cl, NO3 and H2PO4.Assuming that the volume of the cytoplasm Vp is 10% of thatof the whole cell V, the concentrations of K+, Na+, Ca2+, Mg2+,Cl, NO3 and H2PO4 in the cytoplasm averaged70, 15, 13, 4.6, 31, 2.2 and 16 mM, respectively. If the volumeof the cytoplasm was assumed to be 5% of that of the whole cell,their averaged concentrations were 139, 31, 25, 9.2, 62, 4.4and 33 mM, respectively. The averaged ion compositions of thecell sap were K+, 111; Na+, 47; Ca2+, 4.4; Mg2+, 8.9; Cl,91; NO3, 3.3 and H2PO4, 6.0 mM. These values,taking the concentrations and the charges of the protein (Kiyosawa1979b) and amino acids (Sakano and Tazawa 1984) into accountand assuming the presence of some uni- or oligovalent anionsand/or small nonelectrolyte molecules, could explain fairlywell both the electroneutrality and the osmotic pressure ofthe cell, except when Vp/V = 5%. (Received May 18, 1987; Accepted September 29, 1987) 相似文献