AJP - Gastrointestinal and Liver Physiology, Vol 261, Issue 1 50-G56, Copyright © 1991 by American Physiological Society
Link between cell apical morphology and H+ secretion in salamander small intestine
Q. C. Yu and J. F. White
Department of Physiology, Emory University, Atlanta, Georgia 30322.
To determine the morphological basis for the cellular secretion of H+ by in
vitro salamander jejunum the transepithelial proton flux (JH) was measured
under different conditions and compared with the ultrastructure of the
villus absorptive cells using transmission electron microscopy in
conjunction with morphometric analysis. Norepinephrine (NE) stimulated JH
and significantly increased the density of small cytoplasmic vesicular and
tubular profiles in the region immediately below the apical plasma membrane
of the absorptive cells. Cytoplasmic tubular elements were often observed
in direct contact with the plasma membrane at the base of the microvilli,
suggesting that expansion of the plasma membrane had occurred. The alpha
2-antagonist, yohimbine, blocked NE-stimulated H+ secretion and reduced the
number of tubulovesicles. Theophylline reduced the rate of spontaneous acid
secretion and the density of apical tubules and vesicles. Exposure to
horseradish peroxidase revealed a physical connection between the
extracellular space and the apical tubulovesicular compartment. The direct
relationship between the number of apical vesicular and tubular profiles
and JH suggests that the luminal membrane plays a fundamental role in the
cellular events in H+ secretion. The membranes of the tubules and vesicles
may be elements of a dynamic pool of transporting membranes under the
control of exogenous effectors such as catecholamines.
