Fig. 4.

Shorter nsEP are more efficient in recruiting Ca²⁺ from the intracellular stores. (A) The peak amplitude of Ca²⁺ transients evoked by 10-, 60- and 300-ns stimuli was plotted against the stimulus intensity (kV/cm), mean +/− s.e.; n ≥ 15. Cells were stimulated in the presence of 2 mM external Ca²⁺ (red) or its absence (blue). In the latter case, the endoplasmic reticulum was the only significant source of Ca²⁺. Note the increasing contribution of the intracellular Ca²⁺ as the stimulus duration is decreased. (B) The amplitude of Ca²⁺ response due to the discharge from the intracellular stores was plotted against the amplitude of the compound response (due to both the uptake from the outside and the discharge from the stores). The data shown are from the same experiments as in panel (A). For any amplitude of the compound response, shorter stimuli evoked more intracellular Ca²⁺ discharge.