Detection Using SOMA

Interestingly, four plasma samples had a detectable p53 mutation while none were detected in the paired tumour sample. This is most likely to be indicative of multiple independent HCC nodules in these patients, one of which has a p53 mutation. An additional ten plasma samples obtained from healthy US controls were also analysed for the specific p53 mutation. For these samples, a larger amount of plasma (300pl vs. lOOpl for the Chinese samples) was required for DNA extraction in order to obtain a robust wild type signal. No mutations were detected in any of these samples indicating false positives are unlikely to occur using SOMA. The absence of a mutation in five of the plasma samples from patients with a positive tumour sample may be due to insufficient sensitivity and future work will determine the practical limit of detection of the assay. 

Up until now, the SOMA method has been used only in apphcations such as genotyping or variant DNA detection, where PCR-based approaches are available and new high-throughput techniques are under development or being used. Except for applications that require the highest level of accuracy, SOMA will probably not be able to compete with these techniques for these apphcations. 

Evoked stimulation of synaptic transmission has not yet been attempted, although spontaneous endogenous transmission is reported (Baines and Bate 1998). Acetylcholine (ACh) iontophoresis is effective in generating whole-cell current responses in a development-dependent fashion. A 60-M 2 electrode containing 0.1 m ACh (HCl salt Sigma) is positioned within 1-2 j,m of the neuronal soma. A backing current of approximately -2 nA is used to prevent ACh leakage, and an ejection current of approximately +30 nA is used for the iontophoresis. ACh responses are first detected at 13 hours AEL with 25-30%... 

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