Figure 8. Single-channel recordings of N- and P/Q-type channels in spiral ganglion neurons.

A Inward Ba²⁺ currents through single Ca²⁺ channels were recorded in membrane patches from isolated 3-month old SGNs. For recordings of N-type single channel activity, we included a cocktail of Ca²⁺ channel blockers containing: 10 μM nimodipine, 1 μM ω-agatoxin IVA, 200 nM ω-(rSNX-482) and 5 μM mibefradil in the external and patch-electrode solutions. The membrane patch was held at −70 mV and stepped to test voltages indicated above each set of four consecutive traces. The solid dotted lines denote the closed levels. The test potential for the example shown is 5 mV. C Representative current-voltage (I–V) plots for N-type channels show single-channel conductance of 19 ± 2 pS (n = 7). B To record the unitary P/Q-type single channel fluctuations, we included a cocktail of Ca²⁺ channel blockers containing: 10 μM nimodipine, 1 μM conotoxin MVIIA, 200 nM ω-(rSNX-482) and 5 μM mibefradil in the external and patch-electrode solutions. Under outside-out cell-attached configuration, 3-month old SGNs membrane patches were held at −70 mV and stepped to the depolarizing potentials, indicated beside the family of consecutive traces. We used 50 mM Ba²⁺ as the charge carrier. C The amplitude histogram from current traces at 5 mV step potential is shown. Similar data were used to generate the unitary current amplitude-voltage (I–V) plots. D The scattered points of the I–V relation were fitted with a linear regression to determine the conductance of the P/Q channels. For the summary data shown, the single channel conductance (γ) values for P/Q-type channels in 50 mM Ba²⁺ is (in pS): 8.8 ± 1.6 pS (n = 6).