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Elementary [Ca²⁺]_i signals generated by electroporation functionally mimic those evoked by hormonal stimulation

FEDJA BOBANOVI^{b ,d ,a ,c} , MARTIN D. BOOTMAN^{b ,f ,c ,e} , MICHAEL J. BERRIDGE^{b ,f ,c ,e} , NICOLA A. PARKINSON^{b ,a} and PETER LIPP^{b ,a}

<sup>a

b</sup> Laboratory of Molecular Signalling, Babraham Institute, Cambridge, England, U.K.;

<sup>c

d</sup> Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Slovenia; and

<sup>e

f</sup> Department of Zoology, University of Cambridge, Cambridge, England, U.K.

The generation of oscillations and global Ca²⁺ waves relies on the spatio-temporal recruitment of elementary Ca²⁺ signals, such as `Ca²⁺ puffs'. Each elementary signal contributes a small amount of Ca²⁺ into the cytoplasm, progressively promoting neighboring Ca²⁺ release sites into an excitable state. Previous studies have indicated that increases in frequency or amplitude of such hormone-evoked elementary Ca²⁺ signals are necessary to initiate Ca²⁺ wave propagation. In the present study, an electroporation device was used to rapidly and reversibly permeabilize the plasma membrane of HeLa cells and to allow a limited influx of Ca²⁺. With low field intensities (100–500 V/cm), brief (50–100 µs) electroporation triggered localized Ca²⁺ signals that resembled hormone-evoked Ca²⁺ puffs, but not global signals. With such low intensity electroporative pulses, the Ca²⁺ influx component was usually undetectable, confirming that the electroporation-induced local signals represented Ca²⁺ puffs arising from the opening of intracellular Ca²⁺ release channels. Increasing either the frequency at which low-intensity electroporative pulses were applied, or the intensity of a single electroporative pulse (>500 V/cm), resulted in caffeine-sensitive regenerative Ca²⁺ waves. We suggest that Ca²⁺ puffs caused by electroporation functionally mimic hormone-evoked elementary events and can activate global Ca²⁺ signals if they provide a sufficient trigger.—Bobanovi, F., Bootman, M. D., Berridge, M. J., Parkinson, N. A., Lipp, P. Elementary [Ca²⁺]_i signals generated by electroporation functionally mimic those evoked by hormonal stimulation.

Key Words: Ca²⁺ puffs • Ca²⁺ waves • HeLa cells • confocal microscopy • InsP₃ receptors

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