PMID: 8944629Nov 1, 1996Paper

Effects of the intraluminal Ca load on the kinetics of 45Ca uptake and efflux in brain microsomes

The American Journal of Physiology
K M Wells, R F Abercrombie

Abstract

Effects of increasing intraluminal Ca ([Ca]i) on the kinetics of rat brain microsomal uptake and efflux are reported here. Isolated rat brain microsomes accumulated 45Ca in an extravesicular free Ca ([Ca]o)- and ATP-dependent manner. Increased microsomal Ca load resulted in a decreased initial rate of 45Ca uptake and an increased tau, time to reach 63% of steady-state accumulation. Isolated rate brain microsomes lost 45Ca in a temperature- and [Ca]i-dependent manner. Whether preloaded with tracer 45Ca and either < or = 0.5 or 25 microM [Ca]o, the time constant of efflux was larger at 4 degrees C as compared with 37 degrees C. Additionally, increased microsomal Ca load resulted in a decreased time constant of 45Ca efflux. This shorter efflux time constant cannot explain the effect of [Ca]i on tau during uptake which was in fact longer for preloaded microsomes. Rather, these data suggest that, as Ca accumulates into unloaded microsomes, a steadily increasing [Ca]i slows unidirectional Ca influx (presumably by inhibiting the endoplasmic reticulum Ca pump) and enhances unidirectional Ca efflux, and that these combined effects ultimately shorten the time needed to achieve steady-state luminal [Ca]i.

References

Apr 10, 1978·Biochimica Et Biophysica Acta·W Hasselbach
Jan 1, 1979·Annual Review of Biochemistry·L de Meis, A L Vianna
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Feb 15, 1983·The Biochemical Journal·A P Dawson, D V Fulton

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Citations

Mar 28, 1998·The Journal of Biological Chemistry·K M Wells, R F Abercrombie
Jun 6, 2000·American Journal of Physiology. Cell Physiology·X J MengR F Abercrombie

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