Real-time measurements of endogenous CO production from vascular cells using an ultrasensitive laser sensor

Carbon monoxide (CO) has been implicated as a biological messenger molecule analogous to nitric oxide. A compact gas sensor based on a midinfrared las er absorption spectroscopy was developed for direct and real-time measureme nt of trace levels (in approximate pmol) of CO release by vascular cells. T he midinfrared light is generated by difference frequency mixing of two nea rinfrared lasers in a nonlinear optical crystal. A strong infrared absorpti on line of CO (4.61 mum) is chosen for convenient CO detection without inte rference from other gas species. The generation of CO from cultured vascula r smooth muscle cells was detected every 20 s without any chemical modifica tion to the CO. The sensitivity of the sensor reached 6.9 pmol CO. CO synth esis was measured from untreated control cells (0.25 nmol per 10(7) cells/h ), sodium nitroprusside-treated cells (0.29 nmol per 10(7) cells/h), and he min-treated cells (0.49 nmol per 10(7) cells/h). The sensor also detected d ecreases in CO production after the addition of the heme oxygenase (HO) inh ibitor tin protoporphyrin-IX (from 0.49 to 0.02 nmol per 10(7) cells/h) and increases after the administration of the HO substrate hemin (from 0.27 to 0.64 nmol per 10(7) cells/h). These results demonstrate that midinfrared l aser absorption spectroscopy is a useful technique for the noninvasive and real-time detection of trace levels of CO from biological tissues.