Voltage clamping single cells in intact Malpighian tubules of mosquitoes

Principal cells of the Malpighian tubule of the yellow fever mosquito were studied with the methods of two-electrode voltage clamp (TEVC). Intracellul ar voltage (V-pc) was -86.7 mV, and input resistance (R-pc) was 388.5 k Ome ga (n = 49 cells). In six cells, Ba2+ (15 mM) had negligible effects on V-p c, but it increased R-pc from 325.3 to 684.5 k Omega (P < 0.001). In the pr esence of Ba2+, leucokinin-VIII (1 mu M) increased V-pc to 2101.8 mV (P < 0 .001) and reduced R-pc to 340.2 k Omega (P < 0.002). Circuit analysis yield s the following: basolateral membrane resistance, 652.0 k Omega; apical mem brane resistance, 340.2 k Omega; shunt resistance (R-sh), 344.3 k Omega; tr anscellular resistance, 992.2 k Omega. The fractional resistance of the api cal membrane (0.35) and the ratio of transcellular resistance and R-sh (3.5 3) agree closely with values obtained by cable analysis in isolated perfuse d tubules and confirm the usefulness of TEVC methods in single principal ce lls of the intact Malpighian tubule. Dinitrophenol (0.1 mM) reversibly depo larized V-pc from -94.3 to -10.7 mV (P < 0.001) and reversibly increased R- pc from 412 to 2,879 k Omega (P < 0.001), effects that were duplicated by c yanide (0.3 mM). Significant effects of metabolic inhibition on voltage and resistance suggest a role of ATP in electrogenesis and the maintenance of conductive transport pathways.