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Automated patch clamp (APC) instruments enable efficient evaluation of electrophysiologic effects of drugs on human cardiac currents in heterologous expression systems. Differences in experimental protocols, instruments, and dissimilar site procedures affect the variability of IC 50 values characterizing drug block potency. This impacts the utility of APC platforms for assessing a drug's cardiac safety margin. We determined variability of APC data from multiple sites that measured blocking potency of 12 blinded drugs (with different levels of proarrhythmic risk) against four human cardiac currents (hERG [I Kr ], hCav1.2 [L-Type I Ca ], peak hNav1.5, [Peak I Na ], late hNav1.5 [Late I Na ]) with recommended protocols (to minimize variance) using five APC platforms across 17 sites. IC 50 variability (25/75 percentiles) differed for drugs and currents (e.g., 10.4-fold for dofetilide block of hERG current and 4-fold for mexiletine block of hNav1.5 current). Within-platform variance predominated for 4 of 12 hERG blocking drugs and 4 of 6 hNav1.5 blocking drugs. hERG and hNav1.5 block. Bland-Altman plots depicted varying agreement across APC platforms. A follow-up survey suggested multiple sources of experimental variability that could be further minimized by stricter adherence to standard protocols. Adoption of best practices would ensure less variable APC datasets and improved safety margins and proarrhythmic risk assessments.

In this paper, we report on the pharmacological and functional profile of SSR180711 (1,4-Diazabicyclo[3.2.2]nonane-4-carboxylic acid, 4-bromophenyl ester), a new selective alpha7 acetylcholine nicotinic receptor (n-AChRs) partial agonist. SSR180711 displays high affinity for rat and human alpha7 n-AChRs (K(i) of 22+/-4 and 14+/-1 nM, respectively). Ex vivo (3)[H]alpha-bungarotoxin binding experiments demonstrate that SSR180711 rapidly penetrates into the brain (ID(50)=8 mg/kg p.o.). In functional studies performed with human alpha7 n-AChRs expressed in Xenopus oocytes or GH4C1 cells, the compound shows partial agonist effects (intrinsic activity=51 and 36%, EC(50)=4.4 and 0.9 microM, respectively). In rat cultured hippocampal neurons, SSR180711 induced large GABA-mediated inhibitory postsynaptic currents and small alpha-bungarotoxin sensitive currents through the activation of presynaptic and somato-dendritic alpha7 n-AChRs, respectively. In mouse hippocampal slices, the compound increased the amplitude of both glutamatergic (EPSCs) and GABAergic (IPSCs) postsynaptic currents evoked in CA1 pyramidal cells. In rat and mouse hippocampal slices, a concentration of 0.3 muM of SSR180711 increased long-term potentiation (LTP) in the CA1 field. Null mutation of the alpha7 n-AChR gene totally abolished SSR180711-induced modulation of EPSCs, IPSCs and LTP in mice. Intravenous administration of SSR180711 strongly increased the firing rate of single ventral pallidum neurons, extracellularly recorded in anesthetized rats. In microdialysis experiments, administration of the compound (3-10 mg/kg i.p.) dose-dependently increased extracellular acetylcholine (ACh) levels in the hippocampus and prefrontal cortex of freely moving rats. Together, these results demonstrate that SSR180711 is a selective and partial agonist at human, rat and mouse alpha7 n-AChRs, increasing glutamatergic neurotransmission, ACh release and LTP in the hippocampus.