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.

Carbachol increases Na+-HCO3− cotransport activity in murine colonic crypts in a M3−, Ca2+/calmodulin-, and PKC-dependent manner

“…In our study, Ca 2ϩ chelation with BAPTA inhibited the carbachol-mediated increase in NBC activity. To investigate the further function of Ca 2ϩ , we inhibited CaMKII, which is localized in intestinal tissues (48), with KN-62. This kinase promotes anion secretion when introduced into the T84 intestinal cell line (55) and can mediate the activation of Cl Ϫ secretion by Ca 2ϩ -dependent Cl Ϫ channels in respiratory epithelia (14).…”

“…In the kidney, inhibition of Ca 2ϩ /calmodulin-dependent kinase (CaMK) with W-13 prevents cholinergic NBC stimulation (38), whereas calmodulin itself is inhibitory (37). The CaMKII isoform of this enzyme has been demonstrated in the basolateral and apical membranes of the rat jejunum (48), and its introduction into the intestinal cell line T84 induces Cl Ϫ secretion (55). To clarify the role of this enzyme in carbachol-dependent NBC activation in the colon, we therefore studied the effect of CaMKII inhibitor KN-62 (10 M for 10 min).…”

PKA Regulation of Bicarbonate and Lactate Movements Across Rat Jejunal Plasma Membranes

“…Previous studies [1,2,18] provided evidence that the transport systems responsible for bicarbonate and lactate movements across rat jejunal enterocyte are modulated by Ca 2+ /calmodulin (without any involvement of Ca 2+ /calmodulin-dependent protein kinase) and by PKC. The overall action of both Ca 2+ -mediated signaling pathways results in an inhibition of bicarbonate and lactate transports.…”

Thiazide-sensitive NaCl-cotransporter in the Intestine

“…Brush border or basolateral membranes were prepared as previously described by Mg 2ϩ precipitation, followed by differential centrifugation (20,21). Proteins from the kidney (25 g), intestines, brush border membranes, basolateral membranes, or HT-29 cells (100 g) were analyzed by 8% SDS-PAGE followed by Western blotting.…”