The concentration-dependence of CRF-like diuretic peptide: mechanisms of action.
The mechanism of action of synthetic CCRF-DP, the corticotropin-releasing factor (CRF)-related diuretic peptide of the salt marsh mosquito Culex salinarius, was investigated in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. A low concentration of CCRF-DP (10(-9)mol l-1) caused a small but insignificant increase in transepithelial secretion of NaCl and fluid, but significantly reduced transepithelial voltage and resistance without a change in short-circuit current, pointing to the stimulation of passive Cl- transport through the paracellular pathway as the principal mechanism of a mild diuresis. Significant changes in voltage and resistance but not in short-circuit current were duplicated by the ionophore A23187 (0.4 micromol l-1), suggesting Ca2+ as a second messenger at 10(-9)mol l-1 CCRF-DP. A high concentration of CCRF-DP (10(-7)mol l-1) significantly increased transepithelial secretion of NaCl and fluid and significantly increased short-circuit current, pointing to the stimulation of active Na+ transport through the transcellular pathway as the mechanism of a strong diuresis. This effect was mimicked by dibutyryl-cAMP, suggesting cAMP as a second messenger at 10(-7)mol l-1 CCRF-DP. Dibutyryl-cGMP had no effects. These results suggest dose-dependent, receptor-mediated effects of CCRF-DP that target discrete transport pathways via discrete second messengers: low concentrations of CCRF-DP cause a mild diuresis, apparently via Ca2+-mediated effects on paracellular Cl- transport, and high concentrations cause a strong diuresis via cAMP-mediated effects on active transcellular Na+ transport in addition to the effects on the paracellular pathway.
Clark
T M
TM
Department of Zoology, Washington State University, Pullman, WA 99164, USA.
Hayes
T K
TK
Holman
G M
GM
Beyenbach
K W
KW
D000330:Aedes / Q000187:drug effects*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D004231:Diuresis; D004553:Electric Conductivity; D004594:Electrophysiology; D004848:Epithelium / Q000502:physiology; D007301:Insect Hormones / Q000494:pharmacology*; D008317:Malpighian Tubules / Q000187:drug effects* / Q000502:physiology; D015290:Second Messenger Systems; D012965:Sodium Chloride / Q000378:metabolism
D002712:Chlorides; D007301:Insect Hormones; D000001:Calcimycin; D012965:Sodium Chloride; D003994:Bucladesine; D003346:Corticotropin-Releasing Hormone; D002118:Calcium