Figure 4.

Mean I-V relationships of whole-cell currents from oocytes expressing ASIC2-3 measured with a two-electrode voltage clamp. (A) The external solution contains 100 mM NaCl buffered at pH 7.4 or 4.0; voltage range of membrane potential was −100 to 50 mV. (B) The external solution contains 50 mM CaCl₂ without Na⁺, buffered to pH 7.4 or 4.0; voltage range of membrane potential was −100 to 50 mV. Notice the change in the scale of the vertical axis. Inward and outward currents become very small in the absence of Na⁺, and the symbols representing the currents at pH_o 7.4 and 4.0 are almost superimposed. (C) The external solution contains 100 mM NaCl and 50 mM Ca₂Cl buffered at pH 7.4 or 4.0. At pH_o 7.4, no currents are detected; black squares and circles are superimposed. To better observe the effect of Ca²⁺ on both inward and outward currents, the voltage range of the membrane potential was expanded from −150 to 100 mV. Each data point is the mean of three to four oocytes ±SD.