Figure 2. The time constant for receptor current recovery reflects Ca²⁺ extrusion by Na⁺–Ca²⁺ exchange.

Suction pipette recordings from an isolated olfactory receptor cell in response to 1 s stimulation with Ringer solution containing 500 μm IBMX. Same cell as Figure 1. Following IBMX stimulation the cilia were returned to Ringer solution either immediately (A) or following exposure for 1 s (B), 2 s (C), or 3 s (D) to a solution in which the Na⁺ concentration had been reduced to 33 mm (low Na⁺) by equimolar replacement with guanidinium. In each case the rapid decay of receptor current upon the return to Ringer solution has been fitted with a single exponential of time constant A: 0.521 s; B: 0.692 s; C: 0.561 s; D: 0.498 s. Interrupted curves in B–D reproduce the exponential fit to A for comparison. Each trace is the average of 2 or 3 trials and has been junction corrected.