In mammals, a single pannexin1 gene (Panx1) is widely expressed in the CNS 
including the inner and outer retinae, forming large-pore voltage-gated membrane 
channels, which are involved in calcium and ATP signaling. Previously, we 
discovered that zebrafish lack Panx1 expression in the inner retina, with 
drPanx1a exclusively expressed in horizontal cells of the outer retina. Here, we 
characterize a second drPanx1 protein, drPanx1b, generated by whole-genome 
duplications during teleost evolution. Homology searches strongly support the 
presence of pannexin sequences in cartilaginous fish and provide evidence that 
pannexins evolved when urochordata and chordata evolution split. Further, we 
confirm Panx1 ohnologs being solely present in teleosts. A hallmark of 
differential expression of drPanx1a and drPanx1b in various zebrafish brain 
areas is the non-overlapping protein localization of drPanx1a in the outer and 
drPanx1b in the inner fish retina. A functional comparison of the evolutionary 
distant fish and mouse Panx1s revealed both, preserved and unique properties. 
Preserved functions are the capability to form channels opening at resting 
potential, which are sensitive to known gap junction and hemichannel blockers, 
intracellular calcium, extracellular ATP and pH changes. However, drPanx1b is 
unique due to its highly complex glycosylation pattern and distinct 
electrophysiological gating kinetics. The existence of two Panx1 proteins in 
zebrafish displaying distinct tissue distribution, protein modification and 
electrophysiological properties, suggests that both proteins fulfill different 
functions in vivo.