Mechanisms of glutamate activation of axon-to-Schwann cell signaling in the squid.
Membrane potentials from Schwann cells associated with giant axons of the small squid (Alloteuthis and Loliguncula) and the large squid (Loligo) were monitored with glass microelectrodes following 100 Hz/15 s axonal stimulation, or the application of 10(-7) M glutamate and ion substitutions, in the presence or absence of 10(-7) M d-tubocurarine. Glutamate or stimulation caused the membrane of the Schwann cell to depolarize to approximately -32 mV. This was rapidly replaced by a transient hyperpolarization to approximately -55 mV; the potential returning to the resting level (-40 mV) in approximately 7 min. In the presence of d-tubocurarine only the initial depolarization was evident. Nominally zero [Na+]o or treatment with 10(-7) M tetrodotoxin (in normal [Na+]o) blocked the stimulation- and glutamate-induced depolarization while low Clo- hyperpolarized the Schwann cell without effect on the glutamate- or stimulation-induced depolarization. Nao+ depletion or pretreatment with tetrodotoxin in normal Nao+ did not affect the development of the Schwann cell hyperpolarization. These results do not support the hypothesis that the glutamate-induced depolarization is the trigger leading to the Schwann cell hyperpolarization. Preliminary experiments to test the possibility that inositol phosphate second messenger and an increase in [Ca2+]i are triggered by glutamate receptor activation showed that nominally 0 Cao2+/75 mM Mgo2+ only slightly reduced the hyperpolarizing response to stimulation or glutamate while intracellular Bapta (20-30 microM) blocked the hyperpolarization but not the depolarization. [3H]Myoinositol incorporation into axon-Schwann cell plasma membranes was high.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Physiology, School of Medicine, East Carolina University, Greenville, NC 27858.
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Lieberman
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Sanzenbacher
D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D049832:Decapodiformes; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology / Q000379:methods; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D008564:Membrane Potentials / Q000187:drug effects; D012583:Schwann Cells / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D012964:Sodium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014403:Tubocurarine / Q000494:pharmacology
D000613:Aminobutyrates; D002712:Chlorides; D005971:Glutamates; D018698:Glutamic Acid; D013779:Tetrodotoxin; D004533:Egtazic Acid; D012964:Sodium; C012729:2-amino-4-phosphonobutyric acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; D014403:Tubocurarine