Nitric-oxide-synthase-mediated cyclic guanosine monophosphate production in neonatal rat cerebellar prisms is resistant to calcineurin inhibition.
Although the macrolide immunosuppressant tacrolimus (FK506) is neuroprotective in animal models of focal and global cerebral ischaemia, the mechanism of this action is not known. FK506 inhibits the protein phosphatase calcineurin, whose substrates can include nitric oxide synthase (NOS), and the neuroprotective effect of FK506 has been attributed to inhibition of NOS activity. We have examined nitric oxide-mediated cyclic guanosine monophosphate (cGMP) accumulation in neonatal rat cerebellar prisms. As expected, N-methyl-D-aspartate (NMDA) induced a rapid, concentration dependent accumulation of cGMP that was inhibited by the NMDA receptor antagonist dizocilpine (MK801) and the NOS inhibitor L-nitro-arginine methyl ester. Phosphoserine immunopositivity following NMDA exposure was increased in the presence of FK506, confirming inhibition of calcineurin. However, FK506 had no effect on NMDA-stimulated cGMP accumulation. These findings suggest that the neuroprotective effect of FK506 may be mediated by mechanisms other than increased NOS phosphorylation.
Macleod
Malcolm R
MR
Department of Pharmacology, University of Edinburgh, 1 George Square, EH10 5EY, UK. malcolm@apoptosis.freeserve.co.uk
Butcher
Steven P
SP
D000818:Animals; D000831:Animals, Newborn; D002545:Brain Ischemia / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D019703:Calcineurin / Q000378:metabolism; D065095:Calcineurin Inhibitors; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors; D016559:Tacrolimus / Q000494:pharmacology*
D065095:Calcineurin Inhibitors; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D007166:Immunosuppressive Agents; D018696:Neuroprotective Agents; D016194:Receptors, N-Methyl-D-Aspartate; D010768:Phosphoserine; D016202:N-Methylaspartate; D019001:Nitric Oxide Synthase; D019703:Calcineurin; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester; D016559:Tacrolimus