K(+) transport in Malpighian tubules of Tenebrio molitor L: is a K(ATP) channel involved?
The presence of ATP-regulated K(+) (K(ATP)) channels in Tenebrio molitor Malpighian tubules was investigated by examining the effect of glibenclamide on both fluid secretion and basolateral membrane potentials (V(bl)). Glibenclamide, a K(ATP) channel blocker, slowed fluid secretion of Tenebrio tubules. In low bath K(+) concentration (5 mmol l(-1)), glibenclamide either hyperpolarized or depolarized V(bl), resembling the effect seen with Ba(2+). Subsequent addition of 6 mmol l(-1) Ba(2+) caused a further hyper- or depolarization of V(bl). In control Ringer (50 mmol l(-1) KCl, 90 mmol l(-1) NaCl), glibenclamide had no visible effect on V(bl). The effect of ouabain was investigated in low bath [K(+)] in the presence of Ba(2+). V(bl) responded by a small but significant hyperpolarization from -51+/-4 mV to -56+/-4 mV (n=16, P<0.001) in response to 1 mmol l(-1) ouabain. Repeating the experiments in the presence of both glibenclamide and Ba(2+) resulted in a depolarization of V(bl) when ouabain was added. In low bath [K(+)] (high Na(+)), the Na(+)/K(+)-ATPase is expected to function at a high rate. In the presence of Ba(2+), replacing Na(+) by K(+) rapidly depolarized V(bl), but this was followed by a repolarization. Repeating the experiments in the presence of glibenclamide markedly reduced the depolarizing effect and abolished the repolarization, with a gradual decrease in the sensitivity of V(bl) to the surrounding [K(+)]. These results suggest the presence of K(ATP) channels in the basolateral membrane. Glibenclamide had no visible effect on V(bl) in high K(+) or in the absence of Ba(2+), indicating that other highly conductive K(+) channels may mask the effect on K(ATP) channels. This is the first demonstration of the presence of K(ATP) channels in an insect epithelium.
Wiehart
U I M
UI
Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
Klein
G
G
Steels
P
P
Nicolson
S W
SW
Van Kerkhove
E
E
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active; D005905:Glyburide / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D008317:Malpighian Tubules / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013712:Tenebrio / Q000378:metabolism* / Q000502:physiology
D015221:Potassium Channels; D001464:Barium; D010042:Ouabain; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D005905:Glyburide