Leucokinins, a new family of ion transport stimulators and inhibitors in insect Malpighian tubules.
Leucokinins are octapeptides isolated from heads of the cockroach Leucophaea maderae. In the cockroach they increase motility of the isolated hindgut. Surprisingly, synthetic leucokinins have biological activity in a different insect and in a different tissue. In isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti, leucokinins depolarize the transepithelial voltage. This effect on voltage is dependent on extracellular Cl. One leucokinin, LK-8, the effects of which were studied further in isolated Malpighian tubules, was found to inhibit transepithelial fluid secretion at low concentrations (10(-11) M threshold), and to stimulate fluid secretion at high concentrations (3.5 x 10(-9) M threshold). Together, the depolarizing effects on voltage and the stimulation of fluid secretion suggest that leucokinins increase the Cl permeability of the tubule wall thereby increasing the availability of Cl for secretion with Na, K and water. Structure-function comparisons of the seven leucokinins studied suggest that the active region of the octapeptide is segregated to the C-terminal pentapeptide. In view of the known effects of leucokinins on hindgut motility in the cockroach, our finding of effects in mosquito Malpighian tubules suggests that leucokinins may be widely distributed in insects where they may have diverse functions in a variety of organs.
Hayes
T K
TK
Department of Entomology, Texas A&M University, College Station 77840.
Pannabecker
T L
TL
Hinckley
D J
DJ
Holman
G M
GM
Nachman
R J
RJ
Petzel
D H
DH
Beyenbach
K W
KW
D000330:Aedes; D000595:Amino Acid Sequence; D000818:Animals; D002988:Cloaca / Q000502:physiology*; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D007301:Insect Hormones / Q000138:chemical synthesis / Q000494:pharmacology*; D008317:Malpighian Tubules / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology*; D013329:Structure-Activity Relationship
D007202:Indicators and Reagents; D007301:Insect Hormones; D009842:Oligopeptides