Excretion

Central role of metabolism in electrogenesis and epithelial transport in malpighian tubules of the yellow fever mosquito Aedes aegypti

R. Masia 1 , W. Nagel 2 & K. W. Beyenbach 1

1 Dept. of Biomedical Sciences, Cornell University, VRT 8014, Ithaca, NY 14853, USA; 2 Dept. of Physiology, Univ. of Munich, D-80336 Munich, Germany

As soon as dinitrophenol (DNP) enters the peritubular environment of isolated perfused Malpighian tubules of the yellow fever mosquito, the transepithelial voltage plummets from 52.6 mV (lumen-positive) to 6.6 mV, the apical membrane voltage of principal cells falls from -110.6 mV to -8.9 mV, and the basolateral membrane voltage drops from -58.0 mV to -3.3 mV. In parallel, the transepithelial resistance rises to the highest values measured across the epithelium (Pannabecker et al., Am. J. Physiol. 263, R609, 1992). The collapse of all voltages to values less than 10% of control reflects the inhibition of the active transport pathway of Na + and K + through principal cells as transepithelial electrolyte and fluid secretion come to a halt. What astonishes is the absence of simple K + and Na + diffusion potentials across the cell membranes of principal cells in the presence of DNP, which was further explored in principal cells of Malpighian tubules using two-electrode voltage clamp methods (TEVC). DNP, fluoride and cyanide (CN - ) had similar effects, but only the effects of CN - are presented here. CN - (0.3 mM) immediately (and reversibly upon washout) depolarized the intracellular voltage of principal cells (Vpc) from -84.4 to -9.4 mV and increased cell resistance (Rpc) from 408 to 3130 K?. Barium (5 mM), a blocker of K + channels, hyperpolarized Vpc from -86.8 to -101.1 mV and increased Rpc from 408 to 716 K? (reversibly). Bafilomycin (100 µM), which blocks the proton channel of the vacuolar H + -ATPase, depolarized Vpc from -86.8 to -14.0 mV and increased Rpc from 344 K? to 474 K?. Thus, the metabolic blocker CN - increases Rpc nearly 700%, but conventional blockers of K + channels and proton pumps increase Rpc only 76% and 37% respectively. The discrepancy points to major ATP-dependent electrogenic transport systems in addition to the vacuolar H + -ATPase. These ATP-dependent transport systems, channels and electrogenic carriers, may be present in the basolateral and apical membrane of principal cells. (NSF IBN 9604394)

Index terms: metabolic inhibition, principal cells, ATP-dependent transport, cyanide, barium, bafilomycin.

More Topics on the Wing

About Us