Figure 2.

Determination of intracellular Ca²⁺ levels during elevation of extracellular Ca²⁺ in the presence of A23187. (A) Time course of intracellular free Ca²⁺ ([Ca²⁺]_i) during elevation of extracellular Ca²⁺ in the presence of 1 μM A23187 measured by fura-2 fluorescence. Administration of 1 μM A23187 and changes in the extracellular Ca²⁺ concentration, given as pCa_o values, are indicated. Mean values ± SEM (n = 7) of [Ca²⁺]_i determined for the period of 2–4 min after elevation of extracellular Ca²⁺ to the respective value, are shown for pCa_o 5 and 4. (B, left) Activity of Ca²⁺-activated K⁺ channels in a cell-attached patch (test potential = 0 mV) during elevation of extracellular Ca²⁺, given as pCa_o values, in the presence of 1 μM A23187. (right) Channel activity in the same patch after excision (inside-out configuration) at pCa 4 (100 μM) and pCa 6.5 (300 nM). Records were filtered at 500 Hz and digitized at 2 kHz. Unitary current levels are indicated by dashed lines.