AJP - Renal Physiology, Vol 259, Issue 4 580-F586, Copyright © 1990 by American Physiological Society
Glucose absorption by isolated perfused rat proximal straight tubules
J. L. Garvin
Division of Hypertension Research, Henry Ford Hospital, Detroit, Michigan 48202.
Glucose absorption was investigated in isolated perfused proximal straight
tubules from rats by use of a newly developed ultramicrofluorometric assay.
This assay takes advantage of the increase in fluorescence associated with
the reduction of NAD to NADH while glucose is degraded to
6-phosphogluconate. When tubules were perfused at 6.70 +/- 0.42
nl.mm-1.min-1, the mean rate of glucose absorption was 11.0 +/- 1.0
pmol.mm-1.min-1, and the mean rate of fluid absorption was 0.61 +/- 0.06
nl.mm-1.min-1. Glucose transport is generally due to Na-glucose cotransport
in the proximal nephron. In the rat proximal straight tubule, glucose
absorption also appeared to be primarily due to Na-glucose cotransport,
since 10(-4) M phlorizin inhibited absorption by 100%, as did inhibition of
Na(+)-K(+)-ATPase by K removal. To determine the maximum rate of transport,
tubules were perfused at rates greater than 20 nl.mm-1.min-1 with a
solution containing 5.5 mM glucose. The maximum rate of glucose absorption
was approximately 20 pmol.mm-1.min-1 under these conditions. The
concentration of glucose that supports 50% of the maximum rate of
absorption, Km, was 0.6 mM. When tubules were perfused at flow rates of
less than or equal to 2 nl.mm-1.min-1, the luminal glucose concentration
reached a limiting value of 0.47 mM with 5.5 mM glucose in the bath. The
glucose permeability was 3.1 X 10(-6) cm/s.
