AJP - Renal Physiology, Vol 254, Issue 1 139-F144, Copyright © 1988 by American Physiological Society
Protein synthesis inhibitors attenuate water flow in vasopressin-stimulated toad urinary bladder
B. S. Hoch, M. B. Ast, M. J. Fusco, M. Jacoby and S. D. Levine
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Vasopressin stimulates the introduction of aggregated particles, which may
represent pathways for water flow, into the luminal membrane of toad
urinary bladder. It is not known whether water transport pathways are
degraded on removal from membrane or whether they are recycled. We examined
the effect of the protein synthesis inhibitors cycloheximide and puromycin
using repeated 30-min cycles of vasopressin followed by washout of
vasopressin, all in the presence of an osmotic gradient, a protocol that
maximizes aggregate turnover. "High dose" cycloheximide (200 micrograms/ml)
inhibited flow immediately. "Low dose" cycloheximide (1 microgram/ml) did
not affect initial flow; however, flow was inhibited by the fourth
restimulation. On further rechallenge, inhibition persisted but did not
increase. In the absence of vasopressin, inhibition did not develop.
Despite the inhibition of flow in vasopressin-treated tissues, the
cAMP-dependent protein kinase ratio (-cAMP/+cAMP), an index of in vivo cAMP
effect, was elevated in cycloheximide-treated tissues, suggesting
modulation at a distal site in the stimulatory cascade. Cycloheximide
inhibited flow when 10 microM forskolin or 0.2 mM 8-BrcAMP was substituted
for vasopressin in the fourth period; however, MIX (4 mM)-stimulated flow
was enhanced by 1 microgram/ml cycloheximide but inhibited by 200
micrograms/ml cycloheximide. [14C]urea permeability was not inhibited by
cycloheximide. Puromycin (0.5 mM) also inhibited water flow by the fourth
challenge with vasopressin. The data suggest that protein synthesis
inhibitors attenuate flow at a site that is distal to cAMP-dependent
protein kinase.(ABSTRACT TRUNCATED AT 250 WORDS)
