FIGURE 3.

Mutations to 19′. A, homomeric α1^R19′A receptors show evidence of impaired receptor activation. When the α1^R19′A mutation is combined with the α1^Q−26′E mutation in the same subunit (α1^{R19′A/Q−26′E}) and expressed as homomers, the functional impairment was greatest, ablating constitutive activity and markedly reducing conductance. B, heteromeric receptors containing the β^A19′R subunit showed little evidence of functional impairment. When expressed with α1 wild-type (α1β^A19′R) the receptors had similar properties to wild-type α1β heteromers. Similarly, when β^A19′R was co-expressed with α1^Q−26′E the resulting heteromers (α1^Q−26′E-β^A19′R) were little changed compared with the α1^Q−26′E-β heteromers. C, group data summarizing the effects on channel conductance, cluster duration, and intra-cluster shutting frequency for receptors incorporating 19′ mutations. The number of clusters used in the analysis was 284 (α1^R19′A, 4 patches), 378 (α1^R19′Q, 5 patches), 99 (α1^{Q−26′E/R19′A}, 10 patches), 35 (α1β^A19′R, 3 patches), and 133 (α1^Q−26′E-β^A19′R, 5 patches). ***, p < 0.0001; *, p < 0.01.