Figure 5. Capacitance and NCX1 current changes associated with perfusion of PIP₂ into cells in whole-cell voltage clamp.

A, illustration of pipette perfusion method and the reversible effects of perfusing PIP₂ (40 μm) into an A9 cell. Solutions are changed by removing (1) and attaching (2) solution reservoirs (10–50 μl) to a quartz capillary through a silicon sleeve and applying positive air pressure to the reservoir (3). The decrease of capacitance (0.6 pF) corresponds to 5% of the cell capacitance. B, effects of perfusing PIP₂ into a BHK cell expressing NCX1. Outward exchange current is activated by applying 2 mm Ca²⁺ on the extracellular side. With PIP₂ perfusion (40 μm), current increases briefly and then decreases over 2 min in parallel with a 12% decrease of membrane capacitance. C, PIP₂ inhibition of NCX1 currents with physiological ion gradients. Exchange current is defined by application and removal of 4 mm Ni²⁺ in the extracellular solution. I–V relations were taken at points marked a–f. Plots are given for subtracted I–Vs at the start of the experiment (b – a and b – d), during perfusion of PIP₂ (c – d and e – d), and after removal of PIP₂ (f – d).