Figure 3.

S-Type Anion Channel Activation by [Ca²⁺]_cyt in Arabidopsis Guard Cell Protoplasts Requires Preincubation at High [Ca²⁺]_ext Calcium Concentrations.

(A) S-type anion channel currents in a wild-type Arabidopsis guard cell protoplast preincubated in 1 mM [Ca²⁺]_ext with [Ca²⁺]_cyt buffered to 280 nM via the patch pipette solution.

(B) S-type anion channel currents in a guard cell protoplast preincubated in 1 mM [Ca²⁺]_ext with [Ca²⁺]_cyt buffered to 2 μM.

(C) Current-voltage relationships for S-type anion currents recorded from guard cell protoplasts preincubated in 1 mM [Ca²⁺]_ext with [Ca²⁺]_cyt buffered at 280 nM (closed symbols; n = 9) or 2 μM (open symbols; n = 26) as in (A) and (B).

(D) S-type anion channel currents in a guard cell protoplast preincubated in 40 mM [Ca²⁺]_ext with [Ca²⁺]_cyt buffered to 280 nM.

(E) S-type anion channel currents in a guard cell protoplast preincubated in 40 mM [Ca²⁺]_ext with [Ca²⁺]_cyt buffered to 2 μM.

(F) Current-voltage relationships for S-type anion currents recorded from guard cell protoplasts preincubated in 40 mM [Ca²⁺]_ext with [Ca²⁺]_cyt buffered at 280 nM (closed symbols; n =13) or 2 μM (open symbols; n = 8) as in (D) and (E).