Nitric oxide (NO) has proved to be the regulatory molecule of the last decade. Since its identification as the Endothelium Derived Relaxation Factor our love affair with NO has continued with intensity, the number of citations rocketing from a lowly 120 in 1987, to over 5500 last year!
NO is a key modulator of mammalian heart function. It mediates its function through a variety of molecular mechanisms, including regulating cGMP production, by targeting guanylyl cyclase. NO is produced in tissue by nitric oxide synthase (NOS), which uses arginine and oxygen to produce NO. Tinkering with NOS is a good way to find out where NO is regulating a response.
One of the main sources of NO in myocardial tissue is the endocardial endothelium. Fish have a larger ventricle surface area to volume ratio than homeothermic hearts. So, the endocardial endothelium is a potentially rich source of NO for the fish...
