Calmodulin-mediated regulation of bicarbonate and lactate transports in rat jejunum

BACKGROUND/AIMS: Ca(2+)/CaM is known to modulate the activity of several transport systems and its regulation can be accomplished either directly or via the involvement of specific protein kinases. Aim of this study was to investigate the possible role of Ca(2+)/CaM on bicarbonate and lactate transports in rat jejunal enterocyte. METHODS: Enzymatic assays in isolated plasma membranes were performed. Moreover membrane vesicles, transiently opened and resealed, were loaded with Ca(2+) and calmodulin, both in the absence and in the presence of ATP, and were used after that to perform uptake studies. RESULTS: Enzymatic assays gave evidence for the presence of Ca(2+)/CaM-dependent protein kinase II (CaMKII) in plasma membranes from rat jejunum. However, uptake experiments suggest that Ca(2+)/CaM, and not CaMKII, inhibits both basolateral Cl(-)/HCO(3)(-) exchange and H(+)-lactate symport, whilst HCO(3)(-) and Cl(-) conductances are unaffected. Neither Ca(2+)/CaM nor CaMKII seem to regulate brush border Na(+)/H(+) exchanger activity. CONCLUSION: These data are consistent with a Ca(2+)/CaM-mediated reduction of bicarbonate and lactate exit from jejunal enterocyte.