Extracellular calcium concentration controls the frequency of intracellular calcium spiking independently of inositol 1,4,5-trisphosphate production in HeLa cells

Bootman, M. D.; Young, K. W.; Young, J. M.; Moreton, R. B. and Berridge, M. J. (1996). Extracellular calcium concentration controls the frequency of intracellular calcium spiking independently of inositol 1,4,5-trisphosphate production in HeLa cells. Biochemical Journal, 314 pp. 347–354.

DOI: https://doi.org/10.1042/bj3140347

Abstract

Stimulation of single HeLa cells with histamine evoked repetitive increases of the intracellular calcium ion concentration (Ca²⁺ spikes). The frequency of Ca²⁺ spiking increased as the extracellular hormone concentration was elevated. In addition, the frequency of Ca²⁺ spiking could be accelerated by increasing the extracellular Ca²⁺ concentration ([Ca²⁺]₀) in the presence of a constant hormone concentration. The range of [Ca²⁺]₀ over which the spiking frequency could be titrated was nominally-zero to 10mM, being half-maximally effective at approx. 1 and 2.5mM for 37 and 22 °C respectively. The effect of [Ca²⁺]₀ on inositol phosphates production was also examined. Changes of [Ca²⁺]₀ over a range which had been found to affect the frequency of Ca²⁺ spiking did not have any effect on the rate of myo-inositol 1,4,5-trisphosphate (InsP₃) production, although an increase in inositol phosphates production was observed as [Ca²⁺]₀ was increased from zero to values giving less than half-maximal Ca²⁺ spike frequency. These data suggest that at low Ca²⁺ spike frequency, Ca²⁺-stimulated activation of phospholipase C may contribute to Ca²⁺ spiking in HeLa cells, but under some conditions the availability of Ca²⁺ to the intracellular stores, rather than changes in the rate of InsP₃ production, determines the Ca²⁺ spike frequency.

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