Submitted on February 15, 2005
Accepted on April 22, 2005
Characterization of tetraethylammonium uptake across the basolateral membrane of the Drosophila Malpighian (renal) tubule
Mark R Rheault1*, Donna M Debicki1, and Michael J O'Donnell1
1 Department of Biology, McMaster University, Hamilton, Ontario, Canada
* To whom correspondence should be addressed. E-mail: rheaulmr{at}mcmaster.ca.
Basolateral transport of the prototypical type I organic cation tetraethylammonium (TEA) by the Malpighian tubules of Drosophila melanogaster was studied using measurements of basolateral membrane potential (Vbl) and uptake of [14C] labeled TEA. TEA uptake was metabolically dependent and saturable (Jmax, 0.87 pmol tubule-1min-1 ; Kt, 24 µmol l-1). TEA uptake in Malpighian tubules was inhibited by a number of type I (e.g. cimetidine, quinine and TEA) and type II (e.g verapamil) organic cations and was dependent on basolateral membrane potential (Vbl). TEA uptake was reduced in response to conditions which depolarized Vbl (high-K+ saline, Na+-free saline, NaCN) and increased in conditions which hyperpolarized the Vbl (low-K+ saline). Addition of TEA to the saline bathing Malpighian tubules rapidly depolarized the Vbl, indicating that TEA uptake was electrogenic. Blockade of K+ channels with Ba+2 did not block effects of TEA on Vbl, or TEA uptake indicating that TEA uptake does not occur through K+ channels. This is the first study to provide physiological evidence for an electrogenic carrier mediated basolateral organic cation transport mechanism in insect Malpighian tubules. Our results also suggest that the mechanism of basolateral TEA uptake by Malpighian tubules is distinct from that found in vertebrate renal tubules.
