Elevated intracellular Ca2+ acts through protein kinase C to regulate rabbit ileal NaCl absorption. Evidence for sequential control by Ca2+/calmodulin and protein kinase C.

Abstract

Calcium/calmodulin is involved in the regulation of basal rabbit ileal active Na and CI absorption, but the mechanism by which elevated intracellular Ca2" affects Na and Cl transport is unknown. To investigate the roles of the Ca2+/calmodulin and protein kinase C systems in ileal NaCl transport, two drugs, the isoquinolenesulfonamide, H-7, and the naphthalenesulfonamide, W13, were used in concentrations that conferred specificity in the antagonism of protein kinase C (60 MM H-7) and Ca2+/calmodulin (45 MM W13), respectively, as determined using phosphorylation assays in ileal villus cells. W13 but not H-7 stimulated basal active NaCl absorption. H-7 inhibited changes in Na and Cl absorption caused by maximal concentrations of Ca2" ionophore A23187 and carbachol and serotonin, secretagogues that act by increasing cytosol Ca2", while W13 had no effect. In contrast, neither H-7 nor W13 altered the change in NaCl transport caused by the cyclic nucleotides 8-Br-cAMP and 8-Br-cGMP. These data suggest that: (a) basal rabbit ileal NaCl absorption is regulated by the Ca2'/ calmodulin complex and not by protein kinase C; (b) the effect of elevating intracellular Ca2" to decrease NaCI absorption is mediated via protein kinase C but not by Ca2+/calmodulin; (c) the effects of protein kinase C are not overlapping or synergistic with those of Ca2+/calmodulin on either basal absorption or on the effects of increased Ca2+; and (d) neither Ca2+/calmodulin nor protein kinase C are involved in the effects of cAMP and cGMP on ileal active NaCl transport.

Lipopolysaccharide Induces Inhibition of Galactose Intestinal Transport in Rabbits <i>in vitro</i>

“…5A). Similarly, when sugar uptake was determined in the presence of W13, at a concentration of 5x10 -5 M, known to confer specificity for calmodulin antagonism [20], the effect of LPS on the intestinal absorption of the sugar was also practically abolished (Fig. 5B).…”

Isolation of a Member of the Neurotoxin/Cytotoxin Peptide Family from Xenopus laevis Skin Which Activates Dihydropyridine-sensitive Ca2+ Channels in Mammalian Epithelial Cells

“…Lowering [Ca 2ϩ ] i will increase this sodium flux while elevating it inhibits the flux (32). These effects are thought to be mediated through protein kinase C or Ca 2ϩ /calmodulin kinase II (32,33). Most peptides identified from X. laevis skin or skin secretions are homologous to vertebrate hormones and neurotransmitters, providing evidence for the evolutionary relationship of the amphibian skin/ gut/brain axis.…”

Carbachol- and elevated Ca(2+)-induced translocation of functionally active protein kinase C to the brush border of rabbit ileal Na+ absorbing cells.

“…Initially, protein kinase C was suggested as stimulating all Na+/H' exchangers. Now, with few exceptions (27), protein kinase C has been found to inhibit both intestinal and renal apical membrane Na+/H' exchangers but to stimulate their basolateral Na+/H' exchangers (3,26,(28)(29)(30). Whether it is the location in the plasma membrane, the molecular nature of the Na+/H' exchangers, or the subtype of protein kinase C involved which accounts for this differential regulation remains unknown.…”