An apical reduction in [Ca²⁺] reduces the activity of K and Cl channels. Local photolysis of Diazo-2 was used to reduce the [Ca²⁺] specifically at either the basal or apical pole in cells dialyzed with Ca²⁺ to preactivate Ca²⁺-sensitive currents. (A) A bright field and pseudocolored image series is shown from a cell dialyzed with ∼550 nM [Ca²⁺]. After laser exposure, the fluorescence decreased specifically in the apical pole. (B) The kinetic showing the decrease in fluorescence after laser exposure in the apical pole (red line) and basal pole (blue line). (C) The spatial analysis along the yellow line of the peak change in fluorescence compared with the mean of the five previous basal frames. The single-exponential fit is shown in the red line, and the mean of these analysis yields a length constant of 5.02 ± 0.76 µm. (D; top) The decrease in [Ca²⁺] evoked in A resulted in a significant reduction in K⁺ and Cl⁻ conductance (bottom). (E) Paired experiments are shown before and after flash for either 550 or 175 nM [Ca²⁺], “high” or “low” [Ca²⁺], respectively. In F (images) and G (kinetic), basal photolysis of Diazo-2 resulted in a similar decrease in [Ca²⁺] in the basal domain, which again remained localized as demonstrated by the spatial analysis shown in H. (I and J) Basal photolysis failed to reduce either K⁺ or Cl⁻ currents in cells dialyzed with the “high [Ca²⁺]” pipette solution.