Figure 2. The CN-induced inward current (I_CN) is carried by Na⁺ influx.

The magnitude of the inward current induced by 2 mm CN (I_CN) in hypoglossal MNs held at –60 or –70 mV was compared under different experimental conditions (A and C). A, no significant difference (n.s.) in the amplitude of I_CN was found when TTX was present in the aCSF compared to the control condition (control, –51 ± 9 pA, n= 8; TTX, –56 ± 13 pA, n= 7). Blockade of K⁺ currents with TEA and replacement of intracellular K⁺ by Cs⁺ did not change the magnitude of I_CN either (TTX, TEA, CsCl, –62 ± 15 pA, n= 10). Similarly, additional wash-in of Cd²⁺ to block Ca²⁺ conductances did not change I_CN amplitude (TTX, TEA, CsCl, CdCl₂, –46 ± 8 pA, n= 4). B, recording of MN membrane potential (V_m) in the presence of TTX. CN depolarized V_m even when Ca²⁺ was completely removed from the extracellular solution (containing 1 mm EGTA), further indicating that Ca²⁺ was not the charge carrier of I_CN. C, reducing the extracellular Na⁺ concentration from 144 to 26 mm decreased I_CN to 40 ± 13% of the control value (I_CN: control, 45 ± 9 pA; low Na⁺, 18 ± 9; P < 0.05, n= 4); re-addition of Na⁺ increased I_CN back to 76 ± 10%, identifying Na⁺ as the main charge carrier of I_CN at the given membrane potential. (A and B, intracellular solution contained 100 μm fura-2.)