AJP - Cell Physiology, Vol 253, Issue 1 C37-C44, Copyright © 1987 by American Physiological Society
Heterogeneity of expression of apical membrane determinants in A6 epithelial cells
J. B. Moberly and D. D. Fanestil
Expression of apical membrane antigens by A6 cells is heterogeneous. The A6
cell line is a model system for sodium transport and hormone action in
"tight" epithelia. To create probes for the study of sodium transport and
aldosterone action, we generated monoclonal antibodies (MoAbs) by
immunization of BALB/c mice with intact A6 cells. MoAbs binding to apical
membrane determinants were selected by an enzyme-linked immunoadsorbance
assay (ELISA) against the apical surface of confluent A6 monolayers.
Examination of ELISA-positive MoAbs by indirect immunofluorescence on
confluent cells grown on glass cover slips revealed heterogeneity of apical
expression: individual cells comprising the monolayer were fluorescently
labeled to variable degrees and some cells were unlabeled. Expression of
one antigen, recognized by MoAb I4C1, was heterogeneous in cells at low
density as well as for confluent cells. Another antibody, 2B8, exhibited
heterogeneity of labeling in confluent A6 monolayers, but no labeling of
any cells at low density. This heterogeneity of antigen expression
suggested that A6 cells are not a single cell type. However, cloned A6
cells established by limiting dilution were also labeled heterogeneously by
both antibodies. Thus the heterogeneity observed is not due to genetic
inhomogeneity between cells. Expression of the antigens on apical membranes
of cells grown on Millipore filters was heterogeneous for the antigen
recognized by 2B8, but essentially homogeneous for that recognized by I4C1,
suggesting that the degree of differentiation of the cells plays a role in
the heterogeneous expression of apical antigens. This heterogeneity of
expression of apical antigens adds new complexity to the study of A6 cells
and the differentiation of epithelial cells in culture.
