Figure 1.
Measurement of Cm and cytoplasmic free Ca changes during the activation of outward NCX1 currents in a BHK cell. The pipette solution contains 0.5 mM EGTA and 0.25 mM Ca (i.e., 0.4 µM of free Ca), 2 mM ATP, no GTP, and 3 µM Fluo 5N (Kd= 90 µM). When 2 mM Ca is applied for 6 s, the current rises to a peak of 120 pA and decays partially during the Ca application. Cm rises by ∼50% during this time. Peak fluorescence occurs at 5 s and decays toward baseline with a time constant of ∼4 s after deactivation of current. Upon perfusing the pipette tip with 0.5 mM of additional Ca, fluorescence rises to a steady “maximal” level in a nearly linear fashion over 1 min, whereas Cm approximately doubles and then begins to decline, as described in more detail in Fig. 4 (C and D).