Figure 9.

Response adaptation of the cationic current component. The reversal potential of the Cl⁻ current was set at −50 mV, reducing the intracellular Cl⁻ concentration by partial replacement with gluconate. Responses to photorelease of 8-Br-cAMP by two light flashes of the same intensity, interflash interval 20 s. Currents in the same olfactory sensory neuron were measured at the holding potential of +50 mV (top trace) or −50 mV (bottom trace), corresponding to the calculated reversal potential for chloride. Current amplitudes at +50 mV were similar (80 and 81 pA), whereas at −50 mV, the response to the second flash (−8 pA) was reduced to 36% of the response to the first flash (−22 pA). The small size of the CNG-induced inward current is consistent with previous data showing that in the presence of 1 mM external Ca²⁺, the ratio between the CNG current at +50 and −50 mV was ∼4 (Fig. 1 of Kleene, 1995) and indicates that in mouse olfactory sensory neurons, high values of inward current are due to Ca²⁺-activated Cl⁻ current. Similar results were measured in a total of five olfactory sensory neurons.