The mechanism of action of the antidiuretic peptide Tenmo ADFa in Malpighian tubules of Aedes aegypti.
The mechanism of action of Tenebrio molitor antidiuretic factor 'a' (Tenmo ADFa) was explored in isolated Malpighian tubules of Aedes aegypti. In the Ramsay assay of fluid secretion, Tenmo ADFa (10(-9) mol l(-1)) significantly inhibited the rate of fluid secretion from 0.94 nl min(-1) to 0.44 nl min(-1) without significant effects on the concentrations of Na+, K+ and Cl- in secreted fluid. In isolated perfused tubules, Tenmo ADFa had no effect on the transepithelial voltage (Vt) and resistance (Rt). In principal cells of the tubule, Tenmo ADFa had no effect on the basolateral membrane voltage (Vbl) and the input resistance of principal cells (Rpc). Tenmo ADFa significantly increased the intracellular concentration of cyclic guanosine monophosphate (cGMP) from 2.9 micromol l(-1) (control) to 7.4 micromol l(-1). A peritubular [cGMP] of 20 micromol l(-1) duplicated the antidiuretic effects of Tenmo ADFa without inducing electrophysiological effects. In contrast, 500 micromol l(-1) cGMP significantly depolarized V(bl), hyperpolarized Vt, and reduced Rt and Rpc, without increasing antidiuretic potency beyond that of 20 micromol l(-1) cGMP. A plot of peritubular cGMP concentration vs Vbl revealed a steep dose-response between 300 micromol l(-1) and 700 micromol l(-1) with an EC50 of 468 micromol l(-1). These observations suggest a receptor- and cGMP-mediated mechanism of action of Tenmo ADFa. Tenmo ADFa and physiological concentrations of cGMP (< 20 micromol l(-1)) reduce the rate of isosmotic fluid secretion by quenching electroneutral transport systems. The inhibition reveals that as much as 50% of the normal secretory solute and water flux can stem from electrically silent mechanisms in this highly electrogenic epithelium.
Massaro
Richard C
RC
Department of Biomedical Sciences, VRT 8004, Cornell University, Ithaca, NY 14853, USA.
Lee
Lenora W
LW
Patel
Ankit B
AB
Wu
Daniel S
DS
Yu
Ming-Jiun
MJ
Scott
Brett N
BN
Schooley
David A
DA
Schegg
Kathleen M
KM
Beyenbach
Klaus W
KW
D000330:Aedes / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001826:Body Fluids / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D004231:Diuresis / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004577:Electron Probe Microanalysis; D007301:Insect Hormones / Q000494:pharmacology* / Q000502:physiology; D008317:Malpighian Tubules / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D036361:Peptide Hormones / Q000494:pharmacology / Q000502:physiology; D015290:Second Messenger Systems / Q000502:physiology; D013712:Tenebrio / Q000737:chemistry*
D007301:Insect Hormones; D036361:Peptide Hormones; D006152:Cyclic GMP