Inhibition of Sodium-Hydrogen Antiport by Antibodies to NHA1 in Brush Border Membrane Vesicles from Whole Aedes aegypti Larvae.

ABSTRACT

The present research report describes Na+/H+ antiport by brush border membrane vesicles isolated from whole larvae of Aedes aegypti (AeBBMVw). Our hypothesis is that acid quenching of acridine orange by AeBBMVw is predominantly mediated by Na+/H+ antiport via the NHA1 component of the AeBBMVw in the absence of amino acids and ATP. AeNHA1 is a Na+/H+ antiporter that has been postulated to exchange Na+ and H+ across the apical plasma membrane in posterior midgut of A. aegypti larvae. Its principal function is to recycle the H+ and Na+ that are transported during amino acid uptake, e.g., phenylalanine. This uptake is mediated, in part, by a voltage-driven, Na+-coupled, nutrient amino acid transporter (AeNAT8). The voltage is generated by an H+ V-ATPase. All three components, V-ATPase, antiporter, and nutrient amino acid transporter (VAN), are present in brush border membrane vesicles isolated from whole larvae of A. aegypti. By omitting ATP and amino acids, Na+/H+ antiport was measured by fluorescence quenching of acridine orange (AO) caused by acidification of either the internal vesicle medium (Na+in > Na+out) or the external fluid-membrane interface (Na+in < Na+out). Vesicles with 100 micromolar Na+ inside and 10 micromolar Na+ outside or with 0.01 micromolar Na+ inside and 100 micromolar Na+ outside quenched fluorescence of AO by as much as 30%. Acidification did not occur in the absence of AeBBMVw. Preincubation of AeBBMVw with antibodies to NHA1 inhibit Na+/H+ antiport dependent fluorescence quenching, indicating that AeNHA1 has a significant role in Na+/H+ exchange.