Diisopropyl fluorophosphate inhibits receptor-activated Ca2+ influx in isolated rat hepatocytes.
The influence of diisopropyl fluorophosphate (DFP) on receptor-activated increases in cytosolic free Ca2+ concentration ([Ca2+]i) in isolated rat hepatocytes was monitored by measuring phosphorylase a activity and the fluorescence ratio of the Ca2+ sensitive dye Indo-1. Pretreatment (2 min) of hepatocytes with DFP (1 mM) inhibited maximal increases in phosphorylase a activity stimulated by phenylephrine (1 microM), angiotensin II (5 nM), or vasopressin (10 nM) by 36, 35, and 17%, respectively, when the cells were incubated in Ca2+ (1 mM)-containing medium. In contrast, agonist-stimulated increases in phosphorylase a activity were similar in control and DFP-pretreated cells when cells were incubated in medium containing very low (10 nM) Ca2+. Addition of Ca2+ (1 mM) to hepatocytes maintained in the low Ca2+ buffer and exposed to agonists rapidly increased phosphorylase a activity in control cells; however, increases in DFP-pretreated cells were markedly attenuated. Changes in [Ca2+]i similar to those noted with phosphorylase a were observed using Indo-1. Addition of calcium ionophore A23187 to control or DFP-pretreated hepatocytes increased phosphorylase a activity to a similar extent in control and DFP-pretreated cells, demonstrating that DFP pretreatment did not alter the ability of the enzyme to respond to elevation in [Ca2+]i. Collectively, these data indicate that DFP pretreatment of hepatocytes irreversibly inhibits one or more components of the Ca2+ influx pathway.
Richburg
J H
JH
Laboratory for Cellular and Biochemical Toxicology, State University of New Jersey, Piscataway 08855.
Kauffman
F C
FC
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D066298:In Vitro Techniques; D007531:Isoflurophate / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D010762:Phosphorylase a / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D014667:Vasopressins / Q000494:pharmacology
D015220:Calcium Channels; D014667:Vasopressins; D000804:Angiotensin II; D007531:Isoflurophate; D010656:Phenylephrine; D010762:Phosphorylase a