Spontaneous, single channel, chloride currents were recorded in 48% of cell-attached patches on neurones in the CA1 region of rat hippocampal slices. In some patches, there was more than 1 channel active. They showed outward rectification: both channel conductance and open probability were greater at depolarized than at hyperpolarized potentials. Channels activated by gamma-aminobutyric acid (GABA) in silent patches on the same neurones had similar conductance and outward rectification. The spontaneous currents were inhibited by bicuculline and potentiated by diazepam. It was concluded that the spontaneously opening channels were constitutively active, nonsynaptic GABA(A) channels. Such spontaneously opening GABA(A) channels may provide a tonic inhibitory mechanism in these cells and perhaps in other cells that have GABA(A) receptors although not having a GABA(A) synaptic input. They may also be a target for clinically useful drugs such as the benzodiazepines.

The effects on the functional properties of the alpha 1 beta 1 GABAA receptor when the 5' (alpha 1 Val260; beta 1 Ile255) hydrophobic amino acids in the second transmembrane (M2) region were changed to threonine were examined. In response to a saturating concentration of GABA, the current evoked in mutant receptors showed a decreased rate of desensitization and at equilibrium was a greater fraction of the peak current than in wild-type receptors. The half-saturation concentration of the peak current response to GABA in mutant receptors was comparable to that in wild-type receptors, but the Hill coefficient was reduced to less than one. It was concluded that the 5' amino acids in the M2 region have a role in the conformational changes that occur within the alpha 1 beta 1 GABAA receptor in response to GABA.

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ObjectivePatients with previously repaired aortic coarctation (CoA) are at risk of developing late surgical complications. Many patients with CoA also have a bicuspid aortic valve (BAV). We sought to determine in patients with repaired CoA whether the presence of BAV is associated with more cardiovascular reinterventions during follow-up.MethodsAdults with previously repaired simple CoA were recruited from our Adult Congenital Heart Disease database (Sydney, Australia). The incidence of complications relating to the ‘CoA-site’ (descending aortic aneurysm or dissection, or recoarctation) and the ‘AV/AscAo’ (aortic valve or ascending aortic pathology) that required intervention was compared between those with BAV (‘CoA-BAV’) and without BAV (‘CoA-only’).ResultsOf 146 patients with repaired CoA, 101 (69%) had BAV. Age at CoA repair was similar (median 6.0 (IQR 0.5–14.0) years vs 5.0 (IQR 0.5–11.0) years, p=0.44), as was the distribution of repair types, with end-to-end repair the most common in both groups (45.9% vs 45.6%). At a median of 28 years following initial repair, a significantly higher proportion of patients with CoA-BAV required cardiovascular reintervention (45.5% vs 20.0%, p=0.003). Whereas ‘CoA-site’ complications were more common than ‘AV/AscAo’ complications in patients with CoA only (13.3% and 0%, respectively), patients with CoA-BAV had a high prevalence of both ‘CoA-site’ as well as ‘AV/AscAo’ complications (19.8% and 21.8%, respectively). Overall survival was similar (p=0.42).ConclusionIn adults with repaired CoA, patients with CoA-BAV are more than twice as likely to require cardiovascular reintervention by early-to-mid-adult life compared with those with CoA alone. Despite this, no difference in survival outcomes was observed.