Time course of action of pertussis toxin to block the inhibition of stimulated insulin release by norepinephrine

Komatsu, Mitsuhisa, McDermott, Alison, Gillison, Susan and Sharp, Geoffrey (1995) Time course of action of pertussis toxin to block the inhibition of stimulated insulin release by norepinephrine. Endocrinology, 136 (5). pp. 1857-1863. ISSN 0013-7227

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Abstract

Male Sprague-Dawley rats were injected ip with 1 microgram pertussis toxin (PTX)/100 g BW. The rats were killed 24, 48, and 72 h after injection, and their pancreases were removed. At each time point, insulin secretion by isolated islets was measured under basal and glucose-stimulated conditions and in the absence and presence of norepinephrine. cAMP levels were measured under basal and forskolin-stimulated conditions in the absence and presence of norepinephrine. PTX-induced ADP ribosylation of Gi/Go proteins in vivo was monitored by ADP ribosylation in vitro using PTX and 32P-labeled NAD and also by Western blotting. At 24 h, 1 microM norepinephrine inhibited glucose-stimulated insulin secretion by 92% in the control islets, but by only 53% in the PTX-treated islets; at 48 h, norepinephrine still inhibited secretion (by 40%) in the PTX-treated islets; at 72 h, the inhibitory effect of norepinephrine was abolished. Therefore, contrary to recent suggestions, all of the effect of norepinephrine to inhibit insulin release is PTX sensitive. The effects of PTX on the ability of norepinephrine to lower cAMP levels were similar to those observed for the inhibition of insulin release. PTX partially blocked the effect of norepinephrine to lower cAMP levels at 24 and 48 h, and the block was complete after 72 h. The extent of the in vivo ADP ribosylation of the Gi/Go proteins, monitored at each time point by in vitro [32P]ADP-ribosylation and Western blotting, demonstrated a profound ADP ribosylation at 48 and 72 h. As detected by Western blotting, the rates of ADP ribosylation by PTX and the onset of decreased expression varied among the different G-proteins. G alpha o was virtually eliminated after only 24 h of PTX treatment. G alpha i2 was markedly affected by 48 h; G alpha i3 was little affected until 72 h.

Item Type:	Article
Uncontrolled Keywords:	norepinephrine, western blotting, glucose, bodily secretions, forskolin, gtp-binding proteins, rats, sprague-dawley, time factors, toxins, cyclic amp, insulin, rats, pertussis, adp ribosylation
Subjects:	B200 Pharmacology, Toxicology and Pharmacy
Department:	Faculties > Health and Life Sciences > Applied Sciences
Depositing User:	Becky Skoyles
Date Deposited:	24 May 2017 14:41
Last Modified:	12 Oct 2019 17:29
URI:	http://nrl.northumbria.ac.uk/id/eprint/30845

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