1. Low ouabain concentrations in the nanomolar range significantly increased cytosolic free calcium concentration.

2. The ouabain-induced cytosolic free calcium concentration increase was due to transplasmamembrane calcium influx, which could be prevented in the absence of extracellular calcium or by addition of the calcium channel blocker nifedipine.

3. The amount of stored cellular Ca2+, as determined by the thapsigargin-induced cytosolic free calcium concentration increase, was also enhanced by 1 nmol/l ouabain.

4. It is concluded that low ouabain concentrations affect intracellular cytosolic free calcium concentration homoeostasis.

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