Calcium Uptake and Binding by Membrane Fractions of Human Placenta: ATP-dependent Calcium Accumulation

Whitsett, Jeffrey A.; Tsang, Reginald C.

doi:10.1203/00006450-198005000-00012

Cited by 45 publications

(18 citation statements)

References 12 publications

(29 reference statements)

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“…Although Ca-ATPase activity has been demonstrated in human (Miller & Berndt, 1973;Whitsett & Tsang, 1980) and guinea-pig (Shami & Radde, 1971) placental membrane vesicles, it is not clear whether this enzyme is associated with placental calcium transport. It has been shown that the sulphydryl reagent ethacrynic acid, an inhibitor of the Ca-Mg-ATPase (see Schuurmans-Stekhoven & Bonting, 1981) inhibits this enzyme (Shami & Radde, 1971;Miller & Berndt, 1973) as well as ATP-dependent Ca2+ uptake in placental vesicles (Whitsett & Tsang, 1980), whereas ouabain was ineffective on either the enzyme or calcium-uptake activity.…”

Section: Discussionmentioning

confidence: 99%

“…However, these authors discussed their two affinity constants as representing influx (blood to trophoblast) and efflux, since only some of the vesicles were inside-out. Whitsett & Tsang (1980) employed two types of membrane vesicles derived from human placentae: a brush-border fraction and a microsomal fraction which, on the basis of histochemical observations, appear to be related to the fetal side of the trophoblast (Whitsett & Lessard, 1978). These two membranes exhibited ATP-dependent, saturable calcium-uptake kinetics with similar Km values (0-07 and 0 05 x 10-3 mM) and very different Vmax values (1I05 and 0-2 nmol/min .…”

Section: Discussionmentioning

confidence: 99%

“…It has been shown that the sulphydryl reagent ethacrynic acid, an inhibitor of the Ca-Mg-ATPase (see Schuurmans-Stekhoven & Bonting, 1981) inhibits this enzyme (Shami & Radde, 1971;Miller & Berndt, 1973) as well as ATP-dependent Ca2+ uptake in placental vesicles (Whitsett & Tsang, 1980), whereas ouabain was ineffective on either the enzyme or calcium-uptake activity. In a recent study (McKercher, Derewlany & Radde, 1983), the effects of ethacrynic acid (2 mM) on the in vivo transplacental transfer of calcium in the guinea-pig were found to be negative.…”

Section: Discussionmentioning

confidence: 99%

“…Calcium-sodium counter-transport has not been observed in placental membrane vesicles in conditions where ouabain (10-3 M) was present, or in the absence of sodium (Whitsett & Tsang, 1980). In a recent study, the net uptake (arteriovenous difference) ofcalcium by dually perfused guinea-pig placenta was investigated during steady-state perfusion of both maternal and fetal circulations with 45Ca2+ (van Kreel & van Dijk.…”

Section: Yudilevich Unpublished Observations)mentioning

confidence: 99%

“…These observations suggest that calcium is transferred to the fetus by means of active processes which may be regulated by the placenta itself. Little information has been obtained concerning the actual mechanisms involved, except for the identification of Ca-ATPase in guinea-pig (Shami & Radde, 1971) and human (Miller & Berndt, 1973;Whitsett & Tsang, 1980) placental plasma vesicles. However, the localization and orientation of this ATPase in the trophoblast and its function, whether the intracellular regulation of Ca2+ or the transplacental transport of calcium, remains unclear (Whitsett & Tsang, 1980).…”

Section: Introductionmentioning

confidence: 99%

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Asymmetric calcium influx and efflux at maternal and fetal sides of the guinea‐pig placenta: kinetics and specificity.

Sweiry¹,

Yudilevich²

1984

The Journal of Physiology

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SUMMARY1. Unidirectional influx of calcium across maternal and fetal sides of the syncytiotrophoblast was investigated in the guinea-pig placenta by using a rapid (< 30 s) paired-tracer dilution technique. Experiments were performed in an in situ placenta artificially perfused through the umbilical vessels or in an isolated placenta in which both the maternal and fetal circulations were perfused.2. At equimolar Ca2+ concentrations, unidirectional calcium influx was always significantly lower on the maternal side than on the fetal side. Saturation kinetics were observed: on the fetal side the estimated Km was 1 8+007 mm and Vmax was 1-66 + 0-28 /imol/min. g (mean + s.E. of mean) and on the maternal side Km ranged from 0-18 to 1t15 mm and Vmax ranged from 0-12 to 0 59 ,umol/min . g.3. When the inhibition of calcium influx was investigated on the fetal side of the trophoblast by using competing cations, the following sequence was observed:4. Efflux of 45Ca2+ from the trophoblast into the ipsilateral circulation (backflux) was rapid (20-100 % in 6 min) and asymmetric since the fetal: maternal ratio was 1-35+0-11 (mean+S.E. of mean) in the presence of 0.1 mM-Ca2+.5. In the dually perfused placenta, transplacental transfer (6 min) of 45Ca2+ varied over a wide range (0-80 %); however, it was similar to that of the extracellular reference tracer, 22Na+, in either maternal-to-fetal or fetal-to-maternal directions. It is suggested that this is a consequence of the 'leakiness' of the dually perfused placenta since the transplacental transfer of 22Na+ and D-[3H]mannitol (or L-I14C]glucose) measured simultaneously were also variable but similar. Transplacental transfer of 45Ca2+ could not be used to characterize specific calcium-transport mechanisms, whereas highly sensitive trophoblast uptake measurements were provided by the single-circulation, paired-tracer technique.6. Our findings suggest the presence of a specific carrier-mediated transport system for calcium on both maternal and fetal surfaces of the trophoblast. The asymmetries in unidirectional influx into the trophoblast and rapid backflux indicate a mechanism by which the net transfer of calcium from the maternal to the fetal circulation is maintained in favour of the fetus.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Yudilevich Unpublished Observations)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Asymmetric calcium influx and efflux at maternal and fetal sides of the guinea‐pig placenta: kinetics and specificity.

Sweiry¹,

Yudilevich²

1984

The Journal of Physiology

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Bone Disease, Disease of the Parathyroid Glands and Some Other Metabolic Disorders

Walters¹,

Swiet²

2002

Medical Disorders in Obstetric Practice

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Characterization of calcium transport by basal plasma membranes from human placental syncytiotrophoblast

Lafond

Leclerc

Brunette

1991

Journal Cellular Physiology

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We have studied the mechanisms involved in calcium (Ca2+) transport through the basal plasma membranes (BPM) of the syncytiotrophoblast cells from full-term human placenta. These purified membranes were enriched 25-fold in Na+/K(+)-adenosine triphosphate (ATPase), 37-fold in [3H] dihydroalprenolol binding sites, and fivefold in alkaline phosphatase activity compared with the placenta homogenates. In the absence of ATP and Mg2+, a basal Ca2+ uptake was observed, which followed Michaelis-Menten kinetics, with a Km Ca2+ of 0.18 +/- 0.05 microM and Vmax of 0.93 +/- 0.11 nmol/mg/min. The addition of Mg2+ to the incubation medium significantly decreased this uptake in a concentration-dependent manner, with a maximal inhibition at 3 mM Mg2+ and above. The Lineweaver-Burk plots of Ca2+ uptake in the absence and in the presence of 1 mM Mg2+ suggest a noncompetitive type of inhibition. Preloading the BPM vesicles with 5 mM Mg2+ had no significant effect on Ca2+ uptake, eliminating the hypothesis of a Ca2+/Mg2+ exchange mechanism. This ATP-independent Ca2+ uptake was not sensitive to 10(-6) M nitrendipine nor to 10(-4) M verapamil. An ATP-dependent Ca2+ transport was also detected in these BPM, whose Km Ca2+ was 0.09 +/- 0.02 microM and Vmax 3.4 +/- 0.2 nmoles/mg/3 min. This Ca2+ transport requires Mg2+, the optimal concentration of Mg2+ being approximately 1 mM. Preincubation of the membrane with 10(-6) M calmodulin strongly enhanced the initial ATP-dependent Ca2+ uptake. Finally, no Na+/Ca2+ exchange process could be demonstrated.

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Calcium Uptake and Binding by Membrane Fractions of Human Placenta: ATP-dependent Calcium Accumulation

Cited by 45 publications

References 12 publications

Asymmetric calcium influx and efflux at maternal and fetal sides of the guinea‐pig placenta: kinetics and specificity.

Asymmetric calcium influx and efflux at maternal and fetal sides of the guinea‐pig placenta: kinetics and specificity.

Bone Disease, Disease of the Parathyroid Glands and Some Other Metabolic Disorders

Characterization of calcium transport by basal plasma membranes from human placental syncytiotrophoblast

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