Figure 4.

Na⁺/Ca²⁺ exchange currents are reversible in squid ORNs. (A) Current traces from a squid ORN under whole-cell voltage-clamp conditions. The solid line above the current trace indicates the switch from ASW to Tris⁺ ASW. +, 20-mV hyperpolarization. External and internal sodium concentrations are noted above and below the solid line in millimoles per liter⁻¹. Solutions: ASW ext (Tris⁺ ASW)/Na⁺ gluconate int with 4 mM Mg²⁺ and 2 mM ATP. (B) A different ORN exposed to the same protocol as in A, but with Li⁺ gluconate internal solution to eliminate reverse Na⁺/Ca²⁺ exchange. The solid line indicates the switch from ASW to Tris⁺ ASW and back again. Numbers indicate external and internal sodium concentrations in millimoles per liter⁻¹. +, 20-mV hyperpolarizations. Solutions: ASW ext (Tris⁺ ASW)/Li⁺ gluconate int; R_s = 19 MΩ, equilibration time = 5 min). (C) Mean percent decrease in the steady state inward current measured during the switch to Tris ASW under the conditions in A (Na⁺ int) and B (Li⁺ int). *The mean current reduction in Li⁺ gluconate is significantly smaller than Na⁺ gluconate int P < 0.05. Error bars indicate SD; n = numbers of cells.