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Departments of 1 Biomedical Sciences and 2 Agricultural and Biological Engineering, Cornell University, Ithaca, New York 14853; 3 Department of Physiology, University of Munich, D-80336 Munich, Germany; and 4 VERU, Southern Plains Agricultural Research Center, United States Department of Agriculture, College Station, Texas 77845
Principal cells of the Malpighian tubule of
the yellow fever mosquito were studied with the methods of
two-electrode voltage clamp (TEVC). Intracellular voltage
(Vpc) was
86.7 mV, and input resistance
(Rpc) was 388.5 k
(n = 49 cells). In six cells, Ba2+ (15 mM) had negligible effects
on Vpc, but it increased
Rpc from 325.3 to 684.5 k
(P < 0.001). In the presence of Ba2+, leucokinin-VIII (1 µM) increased Vpc to
101.8 mV
(P < 0.001) and reduced Rpc to
340.2 k
(P < 0.002). Circuit analysis yields the
following: basolateral membrane resistance, 652.0 k
; apical membrane
resistance, 340.2 k
; shunt resistance (Rsh),
344.3 k
; transcellular resistance, 992.2 k
. The fractional
resistance of the apical membrane (0.35) and the ratio of transcellular
resistance and Rsh (3.53) agree closely with
values obtained by cable analysis in isolated perfused tubules and
confirm the usefulness of TEVC methods in single principal cells of the
intact Malpighian tubule. Dinitrophenol (0.1 mM) reversibly depolarized
Vpc from
94.3 to
10.7 mV (P < 0.001) and reversibly increased Rpc from 412 to 2,879 k
(P < 0.001), effects that were
duplicated by cyanide (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.
yellow fever mosquito; shunt resistance; potassium channel; barium; leucokinin
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