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Volume 271, Number 42, Issue of October 18, 1996 pp. 26096-26104
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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Temperature-dependent Block of Capacitative Ca²⁺ Influx in the Human Leukemic Cell Line KU-812

(Received for publication, April 18, 1996, and in revised form, July 26, 1996)

The Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, United Kingdom

The mechanism by which depletion of intracellular Ca²⁺ stores activates Ca²⁺ influx is not understood. We recently showed that primaquine, an inhibitor of vesicular transport, blocks the activation of the calcium release-activated calcium current (I_CRAC) in rat megakaryocytes (Somasundaram, B., Norman, J. C., and Mahaut-Smith, M. P. (1995) Biochem. J. 309, 725-729). Since it is well established that vesicular transport is temperature-sensitive, we have investigated the effect of temperature on both the activation and maintenance of store-mediated Ca²⁺ and Mn²⁺ influx in the human leukemic cell line KU-812 using a combination of whole cell I_CRAC recordings and measurements of Mn²⁺ photoquench of fura-2. Activation of I_CRAC was temperature-sensitive, showing a nonlinear reduction when the temperature was lowered from 27 to 17 °C with an abrupt change at 21-22 °C and complete inhibition at 17 °C. Once activated, I_CRAC also displayed an abrupt reduction at 21-22 °C but was not completely blocked even when the temperature was reduced to 14 °C, suggesting that at least one of the temperature-sensitive components is exclusively involved in I_CRAC activation. Activation of store-mediated Mn²⁺ influx also showed similar nonlinear temperature sensitivity and complete inhibition at 19 °C. However, in contrast to I_CRAC measurements, lowering the temperature following maximal activation of the influx pathway at 37 °C did not result in any detectable residual Mn²⁺ entry below 19 °C. We conclude that the mechanism of store-mediated Ca²⁺ influx involves temperature-dependent steps in both its maintenance and activation, suggesting dependence on a lipid membrane environment.

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