Nitric oxide synthase type I (nNOS), vascular endothelial growth factor (VEGF) and myoglobin-like expression in skeletal muscle of Antarctic icefishes (Notothenioidei: Channichthyidae)

The Antarctic icefishes Channichthyidae lack haemoglobin and are thought to lack myoglobin (Mb) in their skeletal muscle as well. Due to the absence of both respiratory pigments, icefishes may present a variety of physiological adaptations in their skeletal muscles. In mammals, molecular responses to limiting oxygen availability in the skeletal muscle include, among others, the over expression of nitric oxide synthases (NOS), such as type I (neuronal nNOS) and type III (endothelial eNOS), as well as the vascular endothelial growth factor (VEGF). In this paper, we evaluated by western blot analysis whether the skeletal muscle of haemoglobin-less icefishes expresses in a constitutive manner higher levels of the type I and type III NOS isoforms and VEGF. Our results demonstrate that haemoglobin-less icefish of the family Channichthyidae do indeed present higher expression of the type I NOS isoform compared with red-blooded Antarctic fish species of other families of the same suborder Notothenioidei. In contrast, VEGF was not over-expressed. Moreover, we show that some icefish species, thought previously to lack Mb in oxidative muscles, actually present Mb-like immunoreactivity in their skeletal muscle.