Bethanechol inhibition of chicken intestinal brush border Na/H exchange: role of protein kinase C and other calcium-dependent processes.
Bethanechol, a muscarinic agonist, inhibits the initial rate of amiloride-sensitive Na uptake by intact mucosa of avian small intestine as well as by isolated chicken villus enterocytes, an effect that is maximal at 90 seconds and reverses by 6 minutes. Bethanechol similarly decreases intracellular pH in isolated cells suspended in bicarbonate-free buffer in a time course similar to inhibition of enterocyte Na uptake, suggesting inhibition of Na/H exchange. In brush border membrane vesicles rapidly prepared from cells stimulated with bethanechol, proton-dependent 22Na uptake is transiently inhibited in a time course similar to inhibition of cell Na uptake. Bethanechol also stimulates transient translocation of protein kinase C from the cytosol to the particulate fraction, a portion of this activity translocating to the brush border membrane. To determine the calcium dependence of bethanechol's action, enterocytes were loaded with varying concentrations of the calcium buffering agent quin-2. Inhibition of cell Na uptake by the calcium ionophore ionomycin could be completely reversed by quin-2 buffering in a concentration-dependent manner. In contrast, quin-2 buffering had little or no effect on the inhibition of Na uptake caused by the protein kinase C activators phorbol esters and oleoylacetylglycerol. Bethanechol's inhibitory effects were partially, but not completely reversed by quin-2 buffering. These data suggest that the effects of bethanechol on chicken villus enterocyte brush border Na/H exchange are mediated by calcium-dependent process(es) as well as by protein kinase C.
Musch
M W
MW
Department of Medicine, University of Chicago, Illinois 60637.
Drabik-Arvans
D
D
Rao
M C
MC
Chang
E B
EB
D000818:Animals; D018723:Bethanechol; D001626:Bethanechol Compounds / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D002645:Chickens; D004848:Epithelium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D007425:Intracellular Membranes / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers
D001626:Bethanechol Compounds; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D018723:Bethanechol; D011493:Protein Kinase C; D002118:Calcium