AJP - Gastrointestinal and Liver Physiology, Vol 238, Issue 2 141-G149, Copyright © 1980 by American Physiological Society
Active secretion of hypoxanthine and xanthine by guinea pig jejunum in vitro
N. Kolassa, W. G. Schutzenberger, H. Wiener and K. Turnheim
Isolated epithelium of guinea pig jejunum secretes hypoxanthine and
xanthine by a transport process that is capable of uphill transport and
dependent on metabolic energy supply. Unidirectional influx of hypoxanthine
across both the luminal and the contraluminal cell membrane appears to be
saturable; influx across the contraluminal membrane is inhibited by
2,4-dinitrophenol (DNP). Efflux across the luminal membrane is diminished
by DNP; efflux across the contraluminal membrane is increased by DNP. This
evidence suggests the existence of a mediated transport system both in the
luminal and the contraluminal cell membrane. Additionally, intracellular
metabolism of hypoxanthine seems to regulate transepithelial permeation:
increased hypoxanthine salvage by the phosphoribosyltransferase reduces the
rate of secretion. However, the incorporation of hypoxanthine into the
nucleotides is limited when the hypoxanthine is added to the luminal side
of the epithelium, and the permeation rate in the absorptive direction is
not markedly influenced by the rate of hypoxanthine salvage. These findings
are a further example of the functional orientation of the jejunal
epithelial cells with respect to enzymic activity and transepithelial
transport properties.
