HEME OXYGENASE-2 AND NITRIC-OXIDE SYNTHASE IN GUINEA-PIG INTRACARDIACNEURONS

THERE is increasing evidence that carbon monoxide (GO), like nitric ox ide (NO), may be a neuronal messenger molecule. This study investigate d the expression of heme oxygenase-2 (HO-2), the enzyme responsible fo r the synthesis of CO, by intracardiac neurones. Many, if not all newb orn guinea-pig intracardiac neurones in culture were HO-2-immunoreacti ve. Furthermore, double labelling showed that a relatively small subpo pulation of these neurones also expressed NO synthase/nicotinamide din ucleotide phosphate (NADPH)-diaphorase (NOS/NADPH-d) activity. These f indings suggest that intracardiac neurones can synthesize CO and that CO may be fundamental to their function. Comparison of the proportions of intracardiac neurones that contain HO-2 with those that express NO S/NADPH-d activity also indicates that CO may be more important than N O in the intrinsic neuronal control of the heart.