Dose-dependent effects of CRF-like diuretic peptide on transcellular and paracellular transport pathways.
The mechanism of action of synthetic Culex corticotropin-releasing factor (CRF)-like diuretic peptide (CCRF-DP) was investigated in isolated, perfused Malpighian tubules of the yellow fever mosquito, Aedes aegypti. Low concentrations of CCRF-DP (10(-10) and 10(-9) M) caused depolarizing oscillations of the lumen-positive transepithelial voltage (Vt) in Malpighian tubules, whereas high concentrations (10(-8) and 10(-7) M) first depolarized and then transiently hyperpolarized Vt; CCRF-DP always lowered transepithelial resistance (Rt), regardless of voltage depolarization or hyperpolarization. The short-circuit current (Isc), an electrical estimate of active transepithelial transport of Na and K, remained unchanged at low concentrations of CCRF-DP, but Isc more than doubled at high concentrations. These effects of CCRF-DP suggest dose-dependent sites of action: low concentrations of CCRF-DP affect the paracellular pathway, and high concentrations affect both paracellular and transcellular pathways.
Clark
T M
TM
Department of Zoology, Washington State University, Pullman 99164, USA.
Hayes
T K
TK
Beyenbach
K W
KW
D000330:Aedes; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D004232:Diuretics / Q000737:chemistry / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D008317:Malpighian Tubules / Q000502:physiology*; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D004232:Diuretics; D010455:Peptides; D003346:Corticotropin-Releasing Hormone; D012964:Sodium; D011188:Potassium