Intracellular Ca indicator Quin-2 inhibits Ca2+ inflow via Nai/Cao exchange in squid axon

Allen, T. J. A.; Baker, P. F.

doi:10.1038/315755a0

Cited by 68 publications

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“…A rapid rate of calcium influx was observed for cells with ATP and a much lower (but measurable) rate of influx by ATP- Figure 4 except that all incubations were extended by 15 Our observations with quin2 ( Figure 5) confirm the finding of Allen and Baker 27 that quin2 inhibits calcium influx by Na-Ca exchange activity. If this action of quin2 on Na-Ca exchange is through its binding of intracellular calcium, as suggested by Allen and Baker, 27 then the sigmoidal behavior may be explained by the gradual activation of Na-Ca exchange as [Ca], rises. Cells with ATP and indol showed a tendency to rupture their sarcolemma at longer times than 30 seconds after calcium addition, preventing an accurate time course determination.…”

Section: Resultsmentioning

confidence: 99%

“…Since quin2 has been reported to inhibit Na-Ca exchange in squid axon, 27 the rate of calcium influx was also measured with indol ( Figure 5B). A rapid rate of calcium influx was observed for cells with ATP and a much lower (but measurable) rate of influx by ATP- Figure 4 except that all incubations were extended by 15 Our observations with quin2 ( Figure 5) confirm the finding of Allen and Baker 27 that quin2 inhibits calcium influx by Na-Ca exchange activity.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Inhibition of calcium influx in isolated adult rat heart cells by ATP depletion.

Haworth¹,

Goknur²,

Hunter³

et al. 1987

Circulation Research

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Using45 Ca, indol, and quin2, calcium uptake was measured in isolated quiescent adult rat heart cells under different metabolic conditions. Exposure of cells in a medium containing 1 mM CaCl 2 to rotenone and uncoupler resulted in adenosine triphosphate (ATP) depletion from 17.08 ± 2.26 to 0.63 ±0.11 nmol/mg within 8 minutes, and the cells went into contracture. In this time, the cells lost 1.65 ± 0.1 nmol Ca/mg of total rapidly exchangeable cellular calcium, and the level of free cytosolic calcium as measured by indol rose from 47.4 ± 16.3 nM to 79.8 ± 27.6 nM. The subsequent rate of rise of intracellular free calcium concentration was just 4 nM/min for at least 40 minutes. Therefore, we investigated the effect of ATP depletion on the rate of calcium entry. In cells loaded with sodium by ouabain treatment without calcium, the initial rate of calcium influx on calcium addition was inhibited by 82-84% when cellular ATP was depleted, as measured by 45 Ca or indol. Quin2 also showed a strong inhibition of calcium influx by ATP depletion, but itself also caused a strong inhibition of calcium influx. The rate of calcium influx declined even further in ATP-depleted cells after the initial influx: Between 1 and 12 minutes after calcium addition, the residual 4SCa uptake rate of the first minute was inhibited by an additional 90%. We conclude that ATP depletion per se does not quickly elevate cytoplasmic free calcium and that such an elevation is prevented by a very strong inhibition of the rate of calcium entry. (Circulation Research 1987;60:586-594) C ellular calcium overload is thought to be a contributing and perhaps decisive factor in heart cell necrosis under a variety of pathologic conditions including hypoxia, ischemia, catecholamine-induced damage, and cardiomyopathy.1 " 3 Therefore, it is desirable to understand how calcium fluxes across the sarcolemma are controlled, and especially how changes in cellular high-energy phosphates affect these fluxes since in many of the above pathologic conditions cellular high-energy phosphates are depleted. Data on this question at present appear to conflict. ATP depletion had no effect on the initial rate of cellular calcium uptake. These results suggest that intracellular calcium levels could rise on ATP depletion, perhaps as a result of an inhibition of energy-dependent calcium efflux or sequestration. On the other hand, rabbit ventricular tissue exposed to hypoxia showed an inhibited rate of 47 Ca influx at the time when hypoxic contracture was induced.9 With aequorin, little or no increase in the level of intracellular free calcium has been found in whole tissue 10 and single cells" when contracture was induced by anoxia or metabolic inhibitors. Anoxic contracture is paralleled by an ATP loss in whole tissue 12 and in isolated adult heart cells' 3 consistent with contracture being caused by a calcium-independent process that is activated by extremely low levels (<100 (xM) of ATP. Thus, these results suggest that very low levels of calcium can be maintained in the face of...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Inhibition of calcium influx in isolated adult rat heart cells by ATP depletion.

Haworth¹,

Goknur²,

Hunter³

et al. 1987

Circulation Research

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“…Therefore, we set the ionic conditions to induce only an outward exchange current by loading [Na] only inside and [Ca] outside. [Ca] i cannot be eliminated because it is necessary for the exchange to operate (Baker, 1972;Baker and McNaughton, 1976;Allen and Baker, 1985;Kimura et al, 1986), so a minimum amount of 100 nM free [Ca]i was added in all the internal solutions. Although it has been reported that the Na-Ca exchange also operates as a Ca-Ca exchange (Blaustein, 1977;Philipson and Nishimoto, 1981;Ledvora and Hegyvary, 1983;Slaughter et al, 1983) and that [Ca]i may inhibit the binding of [Na]i , we assumed that the fraction of Ca-Ca exchange was small enough and that [Ca]i would not compete effectively with [Na] i at 100 nM [Ca] i and 20 mM or higher [Na]i.…”

Section: Resultsmentioning

confidence: 99%

Translocation mechanism of Na-Ca exchange in single cardiac cells of guinea pig.

Kimura

1990

The Journal of General Physiology

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We have studied in single cardiac ventricular cells of guinea pig the ionic translocation mechanism of the electrogenic Na-Ca exchange, i.e., whether Na and Ca ions countercross the membrane simultaneously or consecutively with "ping pong" kinetics. The dose-response relation between the external Ca concentrations ([Ca]o) and the current density of the outward Na-Ca exchange current were measured at three different intracellular Na concentrations ([Nail) in the absence of external Na. Nonlinear regression curves of the dose-response relation obtained by computer revealed Michaelis-Menten type hyperbola from which the [Ca]o giving a half-maximal response (apparent K, Ca o or K'Cao) and the apparent maximum current magnitude (I~x) were estimated at each [Na]i. As [Na]i increased, the K'Cao increased progressively and the value of K'Cao/l'r~ tended to decrease. These results are consistent with the simultaneous mechanism. The K'Cao/l'm~ values, however, were small and close to each other, so it was not possible to completely preclude a consecutive mechanism.

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“…This result is in excellent agreement with the predictions based on measurements of 45Ca fluxes. Allen & Baker (1985) Allen & Baker (1985) have suggested that the inhibition of Na-dependent Ca uptake in squid axons by quin 2 is due to the stabilization of cytosolic Ca at low levels (less than micromolar). One implication of this finding is that Na-dependent Ca uptake would be inoperative in the squid axon at normal low (-01I M) concentrations of cytosolic Ca.…”

Section: Discussionmentioning

confidence: 99%

“…This extra uptake appears to be SODIUM-CALCIUM EXCHANGE IN S YNAPTOSOMES mediated by a Na-Ca exchanger working in the reverse mode (Blaustein & Oborn, 1975), similar to that found in many different types of cells (Blaustein, 1984). Recently, it has been reported that cytosolic quin 2, at concentrations as low as 150 ,uM, selectively inhibits Na-dependent Ca uptake in squid axons (Allen & Baker, 1985 Na-dependent changes in [Ca]i monitored with quin 2, we examined whether quin 2 inhibited Ca uptake in synaptosomes. Fig.…”

Section: Theory: Ca Influx and Effluxmentioning

confidence: 99%

The regulation of cytosolic calcium in rat brain synaptosomes by sodium‐dependent calcium efflux.

Nachshen¹,

Sánchez‐Armass²,

Weinstein³

1986

The Journal of Physiology

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SUMMARY1. When pinched-off presynaptic nerve endings (synaptosomes) isolated from rat brain are incubated in a low-Na (24-36 mM) medium, they take up 45Ca in a time-dependent manner. In a medium containing 1 mM-Ca, this Na-dependent 45Ca uptake amounts to -10 nmol/mg protein at 1 min, and to -40 nmol/mg protein at 20 min. The Na-dependent Ca uptake is not reduced when the synaptosomes are loaded with concentrations of quin 2 as high as 2 mM.2. The increase in 45Ca uptake is paralleled by an increase in the free cytosolic Ca concentration [Ca]j, as monitored with the fluorescent Ca indicators quin 2 or fura 2.[Ca]i increases from the value of 200 to 500 nm within 3-5 min, and thereafter, remains at this elevated level. 3. When synaptosomes that have been loaded with 45Ca (for 1 min, in a low-Na medium) are diluted into an Na-containing medium, there is a rapid efflux of the Ca load. After correcting for Ca that is taken up during the efflux period, calculations show that the total Ca in the synaptosomes returns to the control level within 1 min. Measurements of total chemical Ca parallel the measurements made with radiotracer Ca, and confirm that the Ca loaded into the nerve terminals during a 5 min incubation in a low-Na medium is extruded from the nerve terminals within 1 min in a normal-Na medium.4. The efflux of Ca from the synaptosomes is paralleled by a drop of [Ca]i to its basal level, also within 1 min.5. The mitochondrial uncoupler, carbonyl cyanide p-trifluoromethyloxy-phenylhydrazone (FCCP, 1 /tM), has no effect on either Na-dependent Ca uptake or efflux in synaptosomes. FCCP causes a slight (100-200 nM) increase in [Ca]i in synaptosomes resuspended in either a Na or a low-Na medium. This indicates that little of the Ca that is taken up by the synaptosomes in a low-Na medium is sequestered by the mitochondria.6. These results suggest that Na-dependent Ca efflux (probably Na-Ca exchange) plays an important role in allowing nerve terminals to recover rapidly from a Ca load.

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Intracellular Ca indicator Quin-2 inhibits Ca2+ inflow via Nai/Cao exchange in squid axon

Cited by 68 publications

References 9 publications

Inhibition of calcium influx in isolated adult rat heart cells by ATP depletion.

Inhibition of calcium influx in isolated adult rat heart cells by ATP depletion.

Translocation mechanism of Na-Ca exchange in single cardiac cells of guinea pig.

The regulation of cytosolic calcium in rat brain synaptosomes by sodium‐dependent calcium efflux.

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