Figure 2.

Sensitivity of enzyme activation, receptor binding, and RT-PCR to detect colon carcinoma cells in blood. The indicated number of T84 human colon carcinoma cells were diluted with 10⁶ normal human blood cells in 1 ml and examined for ST (1 μM) activation of guanylyl cyclase and ¹²⁵I-labeled ST (2.5 × 10⁻⁹ M) binding and by RT-PCR using GCC-specific nested primers, as described. PCR was conducted with ³²P-labeled nucleotides, and the resultant amplification products resolved by electrophoresis were stained with ethidium bromide (lower row) or directly quantified (upper row). Fold activation was calculated as (cGMP produced with ST)/cGMP produced without ST). Values represent the mean ± SEM. ND, not detectable.