2. The radical nitric oxide
The free radical (NO) is an inorganic gas that is soluble in aqueous solutions at concentrations of up to 2mM. Since (NO) concentrations do not exceed the low micromolar range under physiological and pathophysiological conditions, many life scientist do not regard (NO) as a gas in biological systems. Due to its small size and lipophilic properties, (NO) can easily cross biological membranes [10].