CHOE, K.P.; O’BRIEN, S.; EVANS, D.H.; TOOP, T.; EDWARDS, S.L.; Univ. of Florida; Univ. of Florida; Univ. of Florida; Deakin University; James Cook University: Immunolocalization of Na⁺/K⁺-ATPase, Carbonic Anhydrase II, and Vacuolar H⁺-ATPase in the Gills of Freshwater Adult Lampreys, Geotria australis

Adult lampreys migrate from seawater into freshwater rivers, where they require branchial ion (NaCl) absorption for osmoregulation. In teleosts and elasmobranchs, pharmological, immunohistochemical, and molecular data support roles for Na⁺/K⁺-ATPase (NaK), carbonic anhydrase II (CAII), and vacuolar H⁺-ATPase (V-ATPase) in two different models of branchial ion absorption. To our knowledge, these transport-related proteins have not been studied in adult freshwater lampreys, and therefore it is not known if they are expressed, or have similar functions, in lampreys. This study was conducted to localize NaK, CAII, and V-ATPase in the gills of adult freshwater lampreys and determine if any of them are expressed in the same cells. We used heterologous antibodies to localize the three proteins in gill tissue from pouched lampreys (Geotria australis). Immunoreactivity (IR) for all three proteins was observed between, and at the base of, gill lamellae in cells that match previous descriptions of mitochondrion-rich-cells (MRCs). NaK-IR was always on the basolateral side of cells that did not stain for CAII or V-ATPase. Alternatively, CAII-IR was always on the apical side of cells that also contained diffuse V-ATPase-IR. Therefore, we have identified two types of MRC in adult freshwater lamprey gills based on immunohistochemical staining for three transport proteins. A model of ion absorption, based on our results, is proposed for adult freshwater lampreys.