Protein kinase C regulation of rat jejunal transport systems: mechanisms involved in bicarbonate absorption.
We examined whether protein kinase C (PKC) modulates the transport systems involved in bicarbonate movements across the plasma membranes of rat jejunum. Results of enzymatic assays provide evidence that under basal conditions conventional PKC (cPKC) is present in both basolateral membranes (BLMs) and apical (brush border) membranes (BBMs) of the enterocyte. In BLMs the basal expression of the kinase is low compared to expression in BBMs; however, treatment with Ca(2+) and phorbol 12-myristate 13-acetate (PMA) causes a significant increase, thus suggesting an asymmetrical kinase translocation. To explore the effect of PKC activation on membrane-bound transport mechanisms, 'in vitro' phosphorylated membrane vesicles were used to perform uptake studies. Results suggest that PKC activation exerts an inhibitory effect on the basolateral Cl(-)-HCO(3)(-) antiporter, whereas the basolateral HCO(3)(-) conductive pathway seems to be stimulated and Cl(-) conductance unaffected. The apical, but not basolateral, Na(+)-H(+) exchanger is inhibited by PKC activation. The specificity of the response to PKC was confirmed by using the kinase inhibitor staurosporine or the inactive phorbol ester 4-alpha-PMA. The inhibition of both apical Na(+)-H(+) and basolateral Cl(-)-HCO(3)(-) exchange activities suggests that the overall action of PKC causes a reduction of transepithelial bicarbonate transport.
Orsenigo
Maria Novella
MN
Dipartimento di Fisiologia e Biochimica Generali, Università di Milano, via Celoria 26, I-20133 Milano, Italy. novella.orsenigo@unimi.it
Tosco
Marisa
M
Baroni
Maurizio Davide
MD
Bazzini
Claudia
C
Laforenza
Umberto
U
Faelli
Alide
A
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001693:Biological Transport, Active; D002712:Chlorides / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000502:physiology*; D007583:Jejunum / Q000201:enzymology* / Q000502:physiology*; D008297:Male; D008871:Microvilli / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D012313:RNA / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism; D005723:gamma-Glutamyltransferase / Q000235:genetics / Q000378:metabolism
D001639:Bicarbonates; D002712:Chlorides; D012313:RNA; D012964:Sodium; D005723:gamma-Glutamyltransferase; D011493:Protein Kinase C; D000254:Sodium-Potassium-Exchanging ATPase