AJP - Cell Physiology, Vol 255, Issue 4 C502-C507, Copyright © 1988 by American Physiological Society
Vasopressin stimulates phosphoinositide hydrolysis in LLC-PK1 cells
L. C. Garg, E. Kapturczak, M. Steiner and M. I. Phillips
Department of Pharmacology, University of Florida, College of Medicine, Gainesville 32610.
LLC-PK1 cells have been shown to possess vasopressin (VP) receptors (V2
type) that are coupled to adenyl cyclase to generate adenosine 3,5'-cyclic
monophosphate (cAMP). To determine whether VP also stimulates
phosphoinositide (PI) hydrolysis to generate inositol phosphate (IP) and
diacylglycerol (DAG) messenger system in LLC-PK1 cells, we measured the
release of IP in LLC-PK1 cells in the absence and presence of various
concentrations of VP. In addition, we also determined the effect of an
increase in osmolality of the incubation medium on VP-stimulated PI
hydrolysis in LLC-PK1 cells. The methods involved the incubation of LLC-PK1
cells with [3H]inositol for its incorporation into membrane PI and the
measurement of the release of [3H]IP in the presence of LiCl which prevents
dephosphorylation. The osmolality of the incubation media was increased
from 300 to 600, 900, and 1,200 mosmol/kgH2O by the addition of NaCl and
urea. In an isosmotic incubation medium, VP (10(-8) M) produced a 100%
increase in PI hydrolysis in LLC-PK1 cells. The effect was much greater at
higher concentrations of the hormone. There was no effect of osmolality in
VP-stimulated PI hydrolysis in LLC-PK1 cells up to 600 mosmol/kgH2O, but PI
hydrolysis decreased significantly when the osmolality of the incubation
medium was increased to 900 or 1,200 mosmol/kgH2O. Our results suggest that
in LLC-PK1 cells, VP stimulates PI hydrolysis probably through VP receptors
that are coupled to phospholipase C. Furthermore, VP-stimulated PI
messenger system in LLC-PK1 cells is influenced by osmolality of the
extracellular fluid.
