Abstract
The effects of Ca 2+, theophylline and promethazine on the phosphorylation of microvillus membrane proteins have been studied in rabbit ileal epithelial cells, using intact cell phosphorylation techniques followed by purification of microvillus membranes, separation of peptides by two-dimensional polyacrylamide gel electrophoresis, and quantitation of phosphorylation by computerized densitometry of autoradiograms. The Ca 2+ ionophore A23187 caused increased phosphorylation of four and possibly five polypeptides; theophylline increased phosphorylation of three peptides, two of which had the same M r and p I values as the peptides altered by the Ca 2+ ionophore; promethazine decreased the phosphorylation of one of the peptides increased by Ca 2+ ionophore. The phosphorylated peptides, which respond similarly to more than one agent which affect ileal Na and Cl absorption, could be involved in the regulation of NaCl absorption either as transport proteins or regulators of transport proteins.
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