Rb. Bajnath et al., ACTIVATION OF ION-TRANSPORT BY COMBINED EFFECTS OF IONOMYCIN, FORSKOLIN AND PHORBOL ESTER ON CULTURED HT-29CL.19A HUMAN COLONOCYTES, Pflugers Archiv, 425(1-2), 1993, pp. 90-99
The differentiated clone 19A of the HT-29 human colon carcinoma cell l
ine was used as a model to study the intracellular electrophysiologica
l effects of interaction of the cAMP, the protein kinase C (PKC) and t
he Ca2+ pathways. (a) A synergistic effect between ionomycin and forsk
olin was observed. From intracellular responses it was concluded that
the synergistic effect is caused by activation of an apical Cl- conduc
tance by protein kinase A and a basolateral K+ conductance by Ca2+. (b
) A transient synergistic effect of ionomycin and the phorbol ester ph
orbol dibutyrate (PDB) was found. The decrease of the response appeare
d to be due to PKC-dependent inactivation of the basolateral K+ conduc
tance. The synergism is caused by PKC-dependent increase of the apical
Cl- conductance and Ca2+-dependent increase of the basolateral K+ con
ductance. (c) The effects of carbachol and PDB were not fully additive
presumably because of their convergence on PKC activation. (d) Forsko
lin and PDB, when added in this order, had a less than additive effect
. Results of cell-attached patch-clamp studies, presented in the accom
panying paper, showed a synergistic effect of forskolin and PDB on non
-rectifying small-conductance Cl- channels. Assuming that these channe
ls are involved in the transepithelial responses it is suggested that
forskolin and PDB induce a modulatory, synergistic increase of the api
cal Cl- conductance when both pathways are activated simultaneously. (
e) The HT-29cl.19A cells differ from T-84 cells in that the latter did
not respond with an increase of the short-circuit current to addition
of phorbol ester. This may be due to a very low expression of PKC alp
ha.