Back to Search Start Over

Activation of glycogen phosphorylase in rat pheochromocytoma PC12 cells and isolated hepatocytes by organophosphates.

Authors :
Kauffman FC
Davis LH
Whittaker M
Source :
Biochemical pharmacology [Biochem Pharmacol] 1990 Jan 15; Vol. 39 (2), pp. 347-54.
Publication Year :
1990

Abstract

Several organophosphates including diisopropylfluorophosphonate (DPF) and a variety of compounds used as chemical warfare agents produced dose- and time-dependent increases in phosphorylase-a, the phosphorylated form of glycogen phosphorylase in rat pheochromocytoma cells, PC12, and isolated hepatocytes. Increases in phosphorylase-a did not occur in cells exposed to the carbamates, physostigmine or pyridostigmine, or to O-ethyl S-2-diisopropylaminoethylmethyl-phosphonathiolate (VX), an organophosphate which is protonated at physiological pH. When extracellular pH was increased to pH 8, VX acted like the other organophosphates and increased phosphorylase-a activity. The possibility that organophosphates increase phosphorylase-a in intact cells by releasing Ca2+ from intracellular binding sites is supported by the following findings: organophosphate-induced increases in phosphorylase-a did not correlate with changes in cyclic AMP in the two cell types studied; in PC12 cells, increases in this activity occurred in the absence of extracellular calcium and were not inhibited by the calcium channel blocker, verapamil; fluorescence of the calcium sensitive dye, Quin-2, in PC12 cells preloaded with the acetoxymethyl ester of the dye was increased by soman; finally, addition of the calcium ionophore, A23187, to PC12 cells maintained in calcium-free medium caused sarin-stimulated phosphorylase-a activity to return rapidly to basal levels. Collectively, these data argue strongly that organophosphates increase phosphorylase-a activity in intact cells via a novel mechanism involving release of calcium from intracellular binding sites.

Details

Language :
English
ISSN :
0006-2952
Volume :
39
Issue :
2
Database :
MEDLINE
Journal :
Biochemical pharmacology
Publication Type :
Academic Journal
Accession number :
2302257
Full Text :
https://doi.org/10.1016/0006-2952(90)90034-i