Figure 8. The effects of noradrenaline on the capsaicin‐activated current are dependent on calcium.

Collected results show the effect of 1 μm noradrenaline on the capsaicin‐activated inward and outward currents with manipulation of external and/or internal calcium. The effect of 1 μm noradrenaline was determined with the following conditions: (1) 2 mm Ca²⁺ in the external solution and 10 mm EGTA in the internal solution (2 Ca²⁺/EGTA); (2) 2 mm Ca²⁺ in the external solution was replaced by 2 mm Mg²⁺ (0 Ca²⁺) and tested with 10 mm EGTA in the internal solution (0 Ca²⁺/EGTA); (3) 2 mm Ca²⁺ in the external solution and 10 mm BAPTA in the internal solution (2 Ca²⁺/BAPTA); (4) 2 mm Ca²⁺ in the external solution was replaced by 2 mm Mg²⁺ (0 Ca²⁺) and tested with 10 mm BAPTA in the internal solution (0 Ca²⁺/BAPTA); (5) 2 mm Ca²⁺ in the external solution was replaced by 2 mm Mg²⁺ (0 Ca²⁺) and tested with 10 mm EGTA in the internal solution after depleting the internal calcium stores by pre‐incubating the cells with 1 μm thapsigargin for 15 min (0 Ca²⁺/thaps/EGTA). A, the inward current was reduced by 55 ± 14% (n = 17) in 2 Ca²⁺/EGTA; by 15 ± 10% (n = 12) in 0 Ca²⁺/EGTA; by 18 ± 15% (n = 6) in 2 Ca²⁺/BAPTA; by 8 ± 3% (n = 10) in 0 Ca²⁺/BAPTA; by 4 ± 3% (n = 6) in 0 Ca²⁺/thaps/EGTA. 2 Ca²⁺/EGTA versus 0 Ca²⁺/EGTA, 2 Ca²⁺/BAPTA, 0 Ca²⁺/BAPTA and 0 Ca²⁺/thaps/EGTA, ^** P < 0.01, one‐way ANOVA followed by Dunnett's post hoc comparison test. B, the outward current was reduced by 49 ± 15% (n = 17) in 2 Ca²⁺/EGTA; by 15 ± 8% (n = 12) in 0 Ca²⁺/EGTA; by 13 ± 11% (n = 6) in 2 Ca²⁺/BAPTA; by 8 ± 3% (n = 10) in 0 Ca²⁺/BAPTA; by −2 ± 3% (n = 6) in 0 Ca²⁺/thaps/EGTA. 2 Ca²⁺/EGTA versus 0 Ca²⁺/EGTA, 2 Ca²⁺/BAPTA, 0 Ca²⁺/BAPTA and 0 Ca²⁺/thaps/EGTA, ^** P < 0.01, one‐way ANOVA followed by Dunnett's post hoc comparison test. C, the capsaicin‐activated inward current was reduced by 55 ± 14% (n = 17) in 1 μm noradrenaline alone, by 59 ± 19% (n = 6) following incubation with 5 μm U73122 (PLC inhibitor) and by 57 ± 14% (n = 6) following incubation with 5 μm U73343 (inactive control). Control versus U73122, P = 0.862; control versus U73343, P = 0.953, one‐way ANOVA followed by Dunnett's post hoc comparison test. D, the capsaicin‐activated outward current was reduced by 49 ± 15% (n = 17) in 1 μm noradrenaline alone, by 49 ± 13% (n = 6) following incubation with 5 μm U73122 and by 58 ± 6% (n = 6) following incubation with 5 μm U73343. Control versus U73122, P = 0.998; control versus U73343, P = 0.352, one‐way ANOVA followed by Dunnett's post hoc comparison test.