title: Differential modulation of cortical synaptic activity by calcineurin (phosphatase 2B) versus phosphatases 1 and 2A.
abstract: Reversible protein phosphorylation is thought to play an important regulatory role in synaptic neurotransmission. We recently have shown in cultured rat cortical neurons that inhibition of the Ca2+/calmodulin-dependent phosphatase calcineurin (phosphatase 2B) increases the frequency, but not the amplitude, of postsynaptic glutamatergic currents, implicating a presynaptic site of action for calcineurin. The specific presynaptic phosphoprotein substrates for calcineurin are unknown, however, calcineurin has been implicated in the control of the Ca2+-independent phosphatases, phosphatases 1 and 2A. To determine whether calcineurin's effects on synaptic transmission are direct or are mediated by changes in phosphatase 1 and/or 2A activities, we used whole-cell voltage clamp to record spontaneous and miniature excitatory postsynaptic currents in the presence of calyculin A (1 microM in bath solution), a membrane permeant inhibitor of phosphatases 1 and 2A which has no effect on calcineurin. Calyculin increased postsynaptic current amplitude without changing current frequency. In these same neurons, subsequent inhibition of calcineurin with cyclosporine A or FK506 had no further effect on current amplitude, but increased current frequency. The increased current amplitude seen with calyculin involved a postsynaptic mechanism, since the effect was reproduced by microcystin (10 microM in pipette solution), which is a membrane-impermeant inhibitor of phosphatases 1 and 2A. Thus, in rat cortical neurons, glutamatergic neurotransmission appears to be frequency-modulated through a presynaptic mechanism by calcineurin, and amplitude-modulated through a postsynaptic mechanism by phosphatases 1 and 2A.
authors.affiliation: The University of Texas Southwestern Medical Center, Molecular Cardiology Laboratories, Dallas 75235-8573, USA. gthomas@ryburn.swmed.edu
authors.forename: G D
authors.initials: GD
authors.lastname: Thomas
authors.forename: B
authors.initials: B
authors.lastname: O'Rourke
authors.forename: R
authors.initials: R
authors.lastname: Sikkink
authors.forename: F
authors.initials: F
authors.lastname: Rusnak
authors.forename: E
authors.initials: E
authors.lastname: Marban
authors.forename: R G
authors.initials: RG
authors.lastname: Victor
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019703:Calcineurin; D002148:Calmodulin-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D054645:Protein Phosphatase 1; D051381:Rats; D017207:Rats, Sprague-Dawley; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000201:enzymology / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D002148:Calmodulin-Binding Proteins; D017661:Receptors, Presynaptic; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1