Effects of dinitrophenol on active-transport processes and cell membranes in the Malpighian tubule of Formica.
In Formica Malpighian tubules KCl secretion is driven by a V-type H+ ATPase in the luminal membrane in parallel with a H+/K+ antiporter. The effect of the protonophore dinitrophenol (DNP) was investigated on the isolated, symmetrically perfused tubule. DNP was applied in two different concentrations: 0.2 mmol/l and 1 mmol/l. The effects were fast and rapidly reversible. The equivalent short-circuit current (Isc) was reduced significantly to respectively 25 +/- 3% Cn = 4) and -3 +/- 7% (n = 11) of the control value when 0.2 mmol/l or 1 mmol/l was added to the bath. When 1 mmol/l DNP was applied the transepithelial resistance (Rte) decreased significantly to 74 +/- 11% of the control value (n = 11), and the luminal over basolateral voltage divider ratio (VDR), providing an estimate of luminal over basolateral membrane resistance, decreased to 37 +/- 12% of the control (n = 6). A concentration of 1 mmol/l DNP was also applied from the lumen. The decrease in Isc was significant, but much less pronounced (74 +/- 5% of control; n = 6) and no significant changes in Rte and VDR were observed. It is argued that, when the concentration in the bath is high enough, DNP may cross the cell and have a protonophoric effect not only on the mitochondria but also across the luminal cell membrane explaining the drop in transepithelial and in relative luminal membrane resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
Dijkstra
S
S
Fysiologie, Limburgs Universitair Centrum, Diepenbeek, Belgium.
Lohrmann
E
E
Van Kerkhove
E
E
Steels
P
P
Greger
R
R
D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors*; D000818:Animals; D001000:Ants; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D002463:Cell Membrane Permeability; D004140:Dinitrophenols / Q000494:pharmacology*; D017136:Ion Transport / Q000187:drug effects*; D008317:Malpighian Tubules / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological
D004140:Dinitrophenols; D000255:Adenosine Triphosphate