Single-channel recording of α7*-nAChR bursts in response to oAβ42 and/or N-Aβ fragment or N-Aβcore in comparison to ACh: effects on single-channel amplitude and burst rate.
We began by investigating the functional interaction between α7*-nAChR and the N-Aβ fragment or the N-Aβcore by determining whether the N-Aβ fragment or N-Aβcore altered α7- or α7β2-nAChR single-channel amplitudes (Figure 2A and 2B; Table 2). No significant α7*-nAChR by treatment interaction was observed for single-channel amplitude (F(7,139) = 0.9; P > 0.05). Further, single-channel amplitudes across all treatment groups were similar between homomeric α7-nAChR and heteromeric α7β2-nAChR (Figures 2A and 2B; Figure S3A; F(1,139) = 0.13; P > 0.05). These data discount the possibilities that single-channel responses induced by oAβ42 or the N-Aβ fragment or N-Aβcore occur via entities other than α7*-nAChR, consistent with earlier work showing blockade of oAβ42 effects by nicotinic antagonists (Liu et al., 2012).
Further, measurements of single-channel burst rates (bursts/sec) were not significantly different between α7*-nAChR subtypes (Figures 2C & 2D; F(7,145) = 0.8; P > 0.05 or across treatments (F(7,139) = 0.9; P > 0.05). Cross-group comparisons revealed that single-channel burst rates were similar between homomeric α7-nAChR and heteromeric α7β2-nAChR (Figure 2C and 2D; Figure S3B; F (7,145) = 0.8; P > 0.05). These data show that when compared to ACh or oAβ42, the application of N-Aβ fragment or N-Aβcore exhibits similar single-channel burst rates when applied alone or in combination with ACh or oAβ42. These findings demonstrate that the rate of single-channel activity is not altered in the exclusive presence of oAβ42, the N-Aβ fragment, or the N-Aβcore or when these Aβ fragments are co-administered with the endogenous ligand, ACh.
Selective enhancement of homomeric α7-nAChR open probability (Popen) in the presence of the N-Aβ fragment
Analyses of Popen revealed a main effect of α7*-nAChR subtype by treatment (Figures 3A & 3B; F(7,145) = 14.7; P<0.0001). Beginning with the homomeric α7-nAChR subtype, within-group analysis showed that α7-nAChR single-channel Popen was greater upon exposure to ACh + N-Aβ fragment relative to responses to ACh alone (P < 0.0001), to N-Aβ fragment alone (P < 0.05), to ACh + N-Aβcore (P < 0.001), or oAβ42 + N-Aβ fragment (P < 0.001). These results demonstrate the ability of the N-Aβ fragment to enhance α7-nAChR Popen when coapplied with endogenous ligand ACh.
Within-group analysis of heteromeric α7β2-nAChR single-channel events showed a significant increase in α7β2-nAChR Popen upon exposure to oAβ42 alone, relative to α7β2-nAChR exposed to ACh alone (Figure 3B). This increase in Popen is similar to α7β2-nAChR exposed to oAβ42 + N-Aβ fragment (P > 0.05), but significantly higher than the Popen in the presence of either N-Aβ fragment or N-Aβcore alone or to oAβ42 + N-Aβcore (P < 0.0001). Statistical analyses also showed a higher Popenfor α7β2-nAChR exposed to oAβ42 + N-Aβ fragment when compared to the N-Aβ fragment alone (P < 0.0001). Exposure to the N-Aβcore alone or in combination with oAβ42 yielded similar single-channel Popen (P > 0.05). Both conditions significantly reduced Popen when compared to oAβ42 alone (P < 0.0001). Further analysis of single-channel Popen revealed a main effect of α7- vs. α7β2-nAChR subtype on single-channel Popenacross all treatment groups (Figure S3E; F(7,145) = 14.7; P < 0.0001). These analyses confirm the increase in α7-nAChR single-channel Popen in the presence of ACh + N-Aβ fragment when compared to the effects of ACh + N-Aβ fragment administration on α7β2-nAChR Popen (P < 0.05). These data also demonstrate the selective effects on α7β2-nAChR over α7-nAChR Popen of exposure to oAβ42alone (P < 0.0001) or to oAβ42 + N-Aβ fragment (P < 0.05). Together, these results further demonstrate the ability of the N-Aβcore to normalize α7β2-nAChR function by reducing α7β2-nAChR Popen in the presence of oAβ42.