AJP - Gastrointestinal and Liver Physiology, Vol 249, Issue 3 422-G426, Copyright © 1985 by American Physiological Society
Evidence for protein kinase C as a regulator of intestinal electrolyte transport
J. D. Fondacaro and L. S. Henderson
We examined the possibility that the Ca2+-and phospholipid-dependent
protein kinase, protein kinase C, may regulate intestinal electrolyte
transport. By use of two active phorbol esters, known activators of protein
kinase C, we studied the secretory response in rat small intestine. In the
in vivo enteropooling assay, 4 beta-phorbol 12-myristate 13-acetate given
by gavage produced intestinal fluid secretion and accumulation comparable
with that of known secretagogues. The response was dose dependent and only
partially blunted at higher doses by atropine. Known inactive phorbol
esters failed to elicit a secretory response. In Ussing chamber
preparations, 4 beta-phorbol 12,13-dibutyrate applied on the serosal side
produced a dose-dependent increase in short-circuit current (Isc). This
response was totally dependent on the presence of Cl ion, and as seen in
vivo atropine only partially attenuated the Isc response to high
concentrations of phorbol ester. Only a minimal increase in Isc was
observed when the ester was applied to the mucosal side. Protein kinase C
was found to phosphorylate the microvillus membrane of the enterocyte, and
the phosphorylation was stimulated by phorbol ester in a
concentration-dependent manner. Two membrane proteins of Mr 51,000 and
46,000 were the primary substrates of the enzyme. These studies demonstrate
that phorbol esters, specific activators of protein kinase C, elicit the
secretory response in rat small intestine both in vivo and in vitro and
that this response is mediated by an increase in Cl ion secretion.
Furthermore, protein kinase C-mediated phosphorylation of specific
microvillus membrane proteins suggests that protein kinase C may modify the
functional state of the microvillus membrane of the enterocyte.
