The differences between the amount of Ca²⁺ release from the Ca²⁺ store and the amount of Ca²⁺ increase in the cytoplasm.

Abstract

Caffeine causes the periodical Ca²⁺ release from the Ca²⁺ store in cultured bullfrog sympathetic ganglion cells. We have already reported that the time course of cytoplasmic Ca²⁺ increment does not reflect faithfully that of Ca²⁺ decrease in the Ca²⁺ store. To understand how this difference arise, the dependency of the amount of Ca²⁺ release from the Ca²⁺ store on caffeine concentration applied was investigated. Dependency of Ca²⁺ increase in cytoplasm on caffeine concentration was different from that of Ca²⁺ decrease in the Ca²⁺ store. At the application of 5mM caffeine, the amount of Ca²⁺ released from the store was half of that at the application of 10mM caffeine, and the amount of cytoplasmic Ca²⁺ increase was about 20%, suggesting that all amount of Ca²⁺ released from the Ca²⁺ store did not cause the cytoplasmic Ca²⁺ increment. [J Physiol Sci. 2006;56 Suppl:S212]