P-type Na+/K+-ATPase and V-type H+-ATPase expression patterns in the osmoregulatory organs of larval and adult mosquito Aedes aegypti

This study describes the expression patterns of P-type Na+/K+-ATPase and V-type H+-ATPase in the larval and adult forms of the mosquito Aedes aegypti and provides insight into their relative importance in ion transport function of key osmoregulatory organs. RT-PCR assays indicate that, at the level of the gene, both ATPases are expressed in all of the osmoregulatory tissues of larvae (midgut, Malpighian tubules, rectum and anal papillae) and adults (stomach, Malpighian tubules, anterior hindgut and rectum). Immunohistochemical studies determined that both ATPases are present in high levels in all the relevant organs, with the exception of the larval rectum (P-type Na+/K+-ATPase only). In larval gastric caeca, ATPase location corresponds to the secretory (basal P-type Na+/K+-ATPase, apical V-type H+-ATPase) and ion-transporting (V-type H+-ATPase on both membranes) regions as previously described. The two ATPases switch membrane location along the length of the larval midgut, indicating three possible regionalizations, whereas the adult stomach has uniform expression of basolateral P-type Na+/K+-ATPase and apical V-type H+-ATPase in each cell. In both larval and adult Malpighian tubules, the distal principal cells exhibit high expression levels of V-type H+-ATPase (apically and cytoplasmically) whereas P-type Na+/K+-ATPase is highly expressed in stellate cells found only in the distal two-thirds of each tubule. By contrast, the proximal principal cells express both P-type Na+/K+-ATPase (basal) and V-type H+-ATPase (apical). These results suggest a functional segregation along the length of the Malpighian tubules based on cell type and region. P-type Na+/K+-ATPase is the only pump apparent in the larval rectum whereas in the larval anal papillae and the adult hindgut (including the anterior hindgut and rectum with rectal pads), P-type Na+/K+-ATPase and V-type H+-ATPase localize to the basal and apical membranes, respectively. We discuss our findings in light of previous physiological and morphological studies and re-examine our current models of ion transport in these two developmental stages of mosquitoes that cope with disparate osmoregulatory challenges.