Figure 7.

α6* nAChRs in sSC neurons are postsynaptic and respond to ambient ACh. A, Whole-cell nAChR responses in α6(+) neurons are postsynaptic. Responses to 1 μm nicotine in α6 L9′S sSC neurons were tested for sensitivity to CNQX (20 μm) and CNQX plus TTX (0.5 μm). Scale bar, 20 pA; 2 s. B, Holding currents in α6(+) sSC neurons exhibits greater membrane conductance fluctuations. sSC α6(+), α6(−), and nontransgenic neurons responding to 100 μm nicotine were recorded in voltage-clamp mode. Representative voltage-clamp records showing membrane conductance fluctuations in the indicated cell type are shown. Scale bar, 6 pA; 600 ms. C, Quantification of membrane conductance fluctuations in α6 L9′S α6(+) and α6(−) sSC neurons. Average root mean square noise for voltage-clamp membrane currents recorded in sSC neurons identified as α6(+) or α6(−) is shown. Data are mean ± SEM. A Student's t test was used to compare α6(−) and α6(+) RMS noise. **p < 0.01. D, Increased membrane conductance fluctuations in α6(+) sSC neurons is blocked by αCtxMII. Identified α6(+) sSC neurons in α6 L9′S slices were recorded in voltage-clamp mode, and membrane conductance fluctuations were observed in the presence of CNQX, CNQX plus TTX, or αCtxMII (100 nm). Scale bar, 6 pA; 600 ms. E, Membrane conductance fluctuations in a6(+) sSC neurons are eliminated by inhibition of ACh release. α6(+) sSC neurons were recorded as in D, and membrane conductance fluctuations were observed in the presence of HC-3 (50 μm) and after drug washout. A representative experiment (n = 2) is shown.