Calmodulin-Mediated Regulation of Bicarbonate and Lactate Transports in Rat Jejunum

Abstract

Background/Aims: Ca²⁺/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 Ca²⁺/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 Ca²⁺ 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 Ca²⁺/CaM-dependent protein kinase II (CaMKII) in plasma membranes from rat jejunum. However, uptake experiments suggest that Ca²⁺/CaM, and not CaMKII, inhibits both basolateral Cl^-/HCO₃^- exchange and H⁺-lactate symport, whilst HCO₃^- and Cl^- conductances are unaffected. Neither Ca²⁺/CaM nor CaMKII seem to regulate brush border Na⁺/H⁺ exchanger activity. Conclusion: These data are consistent with a Ca²⁺/CaM-mediated reduction of bicarbonate and lactate exit from jejunal enterocyte.