Figure 4. Effect of BAPTA loading upon Ca²⁺-dependent activation of whole-cell conductances and a change in intracellular Ca²⁺ in mIMCD-K2 cells.

A, [Ca²⁺]_i in cells grown on coverslips (see Methods) loaded with 5 μM fura-2 AM together with 30 μM BAPTA-AM for 60 min prior to measurement. a, cells superfused with standard bath solution and then exposed to 100 μM ATP failed to show normal Ca²⁺_i transient (representative of 3). b, exposure to 100 nM ionomycin in standard bath solution showed only a limited change in [Ca²⁺]_i up to 10 min but thereafter there was a progressive increase in [Ca²⁺]_i. B, whole-cell currents at ±80 mV in cells preloaded with BAPTA-AM. Cells were preloaded with 30 μM BAPTA-AM for 60 min and then superfused with standard bath solution during whole-cell recording. Stimulation by ATP (a) was without effect (representative of 4 experiments). There was a progressive increase in whole-cell current upon continued exposure to 100 nM ionomycin (b–d). C, biophysical characteristics of whole-cell currents at various times (a–d in B) in BAPTA-loaded cells. Cell was held at 0 mV and pulsed to voltages between ±80 mV for 1 s. Note the marked outward rectification in c and that the time-dependent activation/inactivation of current during voltage pulses depended on [Ca²⁺]_i, this being especially evident in c.