AJP - Renal Physiology, Vol 266, Issue 3 375-F383, Copyright © 1994 by American Physiological Society
Glycogen metabolism in dog inner medullary collecting ducts
L. Meury, J. Senecal, J. Noel and P. Vinay
Departement de Physiologie, Universite de Montreal, Quebec, Canada.
The regulation of glycogen degradation and synthesis in canine inner
medullary collecting ducts (IMCD) was investigated using IMCD tubules
suspensions prepared from dog papilla. A small but significant amount of
glycogen was found in dog IMCD. Under aerobic condition and especially when
no exogenous substrate is available, glycogen breakdown can support IMCD
glycolysis for a short period of time. Increasing concentration of
exogenous glucose but not lactate was able to reduce and even to suppress
(20 mM glucose) the glycogen breakdown. A net synthesis of glycogen was
observed only when the endogenous glycogen pool was previously partially or
totally depleted. Under anaerobic condition, glycogenolysis was stimulated.
The addition of up to 20 mM glucose now reduced but never suppressed this
process. Glycogen metabolism responded to variation in the cells energy
needs, since the net glycogen breakdown was diminished and glycogen
synthesis increased when the cellular ATP turnover was reduced. The reverse
effects were observed when the ATP turnover was increased. At all times,
glycogen metabolism correlated well with changes in tissue glucose
6-phosphate concentration. The energy requirement of IMCD cells and the
availability of alternative energy sources (active mitochondria, exogenous
glucose) are therefore capable of eliciting an integrated and appropriate
response of glycogen phosphorylase and synthase in IMCD tubules in
suspension studied in vitro.
