AJP - Cell Physiology, Vol 263, Issue 4 C759-C766, Copyright © 1992 by American Physiological Society
Regulation of apical Cl- conductance and basolateral K+ conductances by phorbol esters in HT-29cl.19A cells
R. B. Bajnath, M. H. van Hoeve, H. R. de Jonge and J. A. Groot
Department of Experimental Zoology, University of Amsterdam, The Netherlands.
The effect of phorbol esters [4 beta-phorbol 12,13-dibutyrate (PDB) and
phorbol 12-myristate 13-acetate (PMA)] on potential differences and
resistances was studied with the conventional microelectrode technique
applied to confluent filter-grown monolayers of the human colon carcinoma
cell line HT-29cl.19A. Phorbol esters (PDB or PMA from 10(-7) to 10(-6) M)
evoked 1) a transient increase in the transepithelial potential difference
(peak value 3.5 +/- 0.5 mV), 2) a depolarization of the cell potential by
23 +/- 2 mV at the peak of the transepithelial potential change and a
continued decrease during the decline of the transepithelial potential, and
3) a decrease of the fractional resistance of the apical membrane
consisting of two phases, a relative rapid one (time constant 1.2 +/- 0.2
min) and a much slower further decrease during the second phase (time
constant 34 +/- 1 min). Ion replacements and electrical circuit analyses
indicate that PDB activates an apical Cl- conductance and slowly inhibits
the basal K+ conductance of the basolateral membrane. PDB reduced the
transepithelial response to forskolin due to inhibition of the basal K+
conductance. The Ca2+ ionophore ionomycin accelerated that effect of PDB.
Staurosporine inhibited the effects of PDB, suggesting that the PDB effects
are mediated via activation of a protein kinase C.
