Proton pumps in fish gill pavement cells?

The gill epithelium which comprises several types of cell faces multiple functions (O2/CO2 transfer, acid-base balance and ionic regulation). Little is known of the respective cellular localization of these functions. TEM examination of the catfish gill shows, in pavement cells, cytoplasmic vesicles and apical pits, both ornamented with studs reminiscent of the proton pumps observed in H+ secretory epithelia. Ornamented apical pits are more frequently observed in acidotic fish. Taking together with our previous studies, this finding suggests that pavement cells play an important role, in addition to transfer of gas, by secreting protons. A new model of gill exchanges is proposed.