*A–C*, bradykinin-induced VSOR currents in the presence of intracellular EGTA at 10 m

m (

*A*), BAPTA at 1 m

m (

*B*) and BAPTA at 10 m

m (

*C*). Voltage pulse protocols were the same as those in . The Ca

^{2+} chelators were applied via patch pipettes.

*D, I–V* relationships at different concentrations of intracellular Ca

^{2+} chelators. The numbers of the cells analysed were 17 for 1 m

m EGTA (open squares), 15 for 10 m

m EGTA (open circles), 13 for 1 m

m BAPTA (filled circles), 14 for 10 m

m BAPTA (filled squares) and 16 for 10 m

m BAPTA observed after pretreatment with 1 μ

m thapsigargin and removal of extracellular Ca

^{2+} (filled triangles). Significant suppression in the amplitude at +100 mV was seen only in the presence of 10 m

m BAPTA (filled squares and triangles;

*P* < 0.05 by multiple comparisons).

*E*, model of steady-state spatial [Ca

^{2+}]

_{i} profiles of a single ‘Ca

^{2+} nanodomain’ in the presence of Ca

^{2+} chelators at different concentrations. The profiles were drawn based on the equation proposed by :

where

,

*r* is the distance from a Ca

^{2+} channel pore,

*i*_{Ca} is the single-channel Ca

^{2+} current (0.1 pA, assuming that

*i*_{Ca} through a TRPC channel is slightly smaller than that through a voltage-gated Ca

^{2+} channel),

*F* is the Faraday constant,

*D*_{Ca} is the diffusion coefficient of free Ca

^{2+} (223 μm

^{2} s

^{−1}; ), λ is the length constant of the profile,

*k*_{Bon} is the Ca

^{2+} binding rate constant of the chelator (2.5 × 10

^{6}m^{−1} s

^{−1} for EGTA, 5 × 10

^{8}m^{−1} s

^{−1} for BAPTA; ), [B] is the concentration of the Ca

^{2+}-free chelator, [B

_{T}] is the total concentration of the chelator, and

*K*_{D} is the dissociation constant of the chelator (0.438 μ

m, based on the

*in vivo* calibration of a BAPTA-type Ca

^{2+} indicator by ; the

*K*_{D} values of EGTA and BAPTA are assumed to be the same). [Ca

^{2+}]

_{i}(∞) must be the basal [Ca

^{2+}]

_{i} in the bulk cytoplasm (0.1 μ

m). Note that [Ca

^{2+}]

_{i} is plotted on a logarithmic scale. The calculated λ values were 331 nm, 105 nm, 23.4 nm and 7.4 nm in the presence of 1 m

m EGTA, 10 m

m EGTA, 1 m

m BAPTA and 10 m

m BAPTA, respectively. The profile in the absence of chelators, indicated by the dotted line, was calculated by putting λ at infinity, i.e. making the exponential term unity.

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