Figure 6.

Evoked [Ca²⁺]_i rise is facilitated by Ca²⁺ release from intracellular stores. A, Fura-2 fluorescence quenching recorded on f₃₆₀. Data are from one guard cell recorded after intracellular loading with Mn²⁺ in 20 mm K⁺-Mes, pH 6.1, and 2 mm MnCl₂. Voltage steps of 20 s to −200 mV (⊔, above) applied with the cell bathed in 20 mm K⁺-Mes, pH 6.1, plus 2 mm CaCl₂, then in the same buffer without CaCl₂ (open bar), and finally with 2 mm MnCl₂ (striped bar). Inset, f₃₆₀ during the first 20 s after voltage steps without (○) and with (•) Ca²⁺ outside after normalizing to the fluorescence signal at the start of each voltage step. Note the rapid decay in f₃₆₀ after voltage stimulus in the presence of external Ca²⁺. B to D, [Ca²⁺]_i rise was suppressed by 10 μm ryanodine (B) and augmented by 100 μm heparin (C) and 1 mm neomycin sulfate (D). Data are from three guard cells in 5 mm Ca²⁺-Mes, pH 6.1, with 10 mm KCl. Membrane voltages were clamped to −50 mV in each case. Voltage steps to −200 mV (B) and −180 mV (C and D) are indicated above (⊔). Times of treatments with ryanodine, heparin, and neomycin sulfate are indicated by the open bars in each case. Note the prolonged secondary rise in [Ca²⁺]_i in the presence of heparin and neomycin sulfate.