BILIRUBIN INDUCES A CALCIUM-DEPENDENT INHIBITION OF MULTIFUNCTIONAL CA2+ CALMODULIN-DEPENDENT KINASE-II ACTIVITY IN-VITRO/

Citation
Sb. Churn et al., BILIRUBIN INDUCES A CALCIUM-DEPENDENT INHIBITION OF MULTIFUNCTIONAL CA2+ CALMODULIN-DEPENDENT KINASE-II ACTIVITY IN-VITRO/, Pediatric research, 38(6), 1995, pp. 949-954
Citations number
41
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pediatrics
Journal title
ISSN journal
0031-3998
Volume
38
Issue
6
Year of publication
1995
Pages
949 - 954
Database
ISI
SICI code
0031-3998(1995)38:6<949:BIACIO>2.0.ZU;2-X
Abstract
Excessive bilirubin levels in newborn infants result in long term neur ologic deficits that remain after bilirubin levels return to normal. M uch of the observed neurologic deficits can be attributed to bilirubin -induced, delayed neuronal cell death. Inhibition of calcium/calmoduli n-dependent kinase II (CaM kinase II1) activity that precedes cell dea th is observed in conditions such as seizure activity, stroke, and glu tamate excitotoxicity. Because neonatal bilirubin exposure results in neuronal loss in developing brain systems, we tested whether bilirubin exposure would induce an immediate inhibition of CaM kinase II activi ty, in vitro. P-81 filtration assay of basal and calcium-stimulated ki nase activity was performed under standard kinase assay conditions. Bi lirubin and/or albumin was added to the reaction vessels to determine the effect of these agents on kinase activity. Bilirubin exposure resu lted in a concentration-dependent inhibition of CaM kinase II activity (IC50 = 16.78 mu M). At concentrations above 50 mu M, bilirubin expos ure resulted in a 71 +/- 8% (mean +/- SD) inhibition of kinase activit y (p < 0.001, t test, n = 10). Bilirubin exposure did not results in k inase inhibition if excessive bilirubin was removed by albumin binding before stimulation of kinase activity (106.9 +/- 8.6% control activit y, n = 5), However, removal of bilirubin by binding with albumin after calcium addition did not restore kinase activity, (36.1 +/- 3.8% cont rol activity, n = 5). Thus, once inhibition was observed, the activity could not be restored by addition of albumin. The data suggest that b ilirubin exposure resulted in a calcium-dependent inhibition of CaM ki nase II activity that, once induced, was not reversible by removing bi lirubin by the addition of albumin, Because inhibition of CaM kinase I I activity has been correlated with delayed neuronal cell death in man y neuropathologic conditions, bilirubin-induced inhibition of this enz yme may be a cellular mechanism by which bilirubin exposure results in delayed neuronal cell death in developing brain.