Extracellular high K+ stimulates vesicular glutamate release from astrocytes by activating voltage-dependent calcium channels.
Extracellular high K(+) (75 mM) increased intracellular Ca(2+) concentrations in cultured rat hippocampal astrocytes, and the Ca(2+) rise was abolished by deleting extracellular Ca(2+) or cadmium, a non-selective inhibitor of voltage-dependent calcium channels (VDCCs). In the reverse transcription-polymerase chain reaction analysis, cultured astrocytes expressed mRNAs for L type-VDCC subunits such as alpha1B, alpha1C, alpha1D, and alpha1E. Extracellular high K(+) (75 mM) stimulated glutamate release from astrocytes. The glutamate release was not prevented by the glutamate transporter inhibitor, L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC), or deleting extracellular Na(+), but otherwise it was clearly inhibited by deleting extracellular Ca(2+), cadmium, vesicular transport inhibitors such as brefeldin A, bafilomycin A1, and latrunculin B, or botulinum toxin-A, an exocytosis inhibitor. Extracellular high K(+) (75 mM) bleached fluorescent signals of FM1-43, taken up into the vesicular membrane in astrocytes, that was also inhibited by deleting extracellular Ca(2+), cadmium, brefeldin A, bafilomycin A1, latrunculin B, or botulinum toxin-A, but not by PDC. Taken together, the results of the present study indicate that extracellular high K(+)-evoked depolarization activates VDCCs expressed in astrocytes, causing an increase in intracellular Ca(2+) concentrations through VDCCs, which triggers vesicular glutamate release from astrocytes, independently of reverse transport through glutamate transporters.
Yaguchi
Takahiro
T
Division of Bioinformation, Department of Physiology, Hyogo College of Medicine, Nishinomiya, Japan.
Nishizaki
Tomoyuki
T
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology; D015640:Ion Channel Gating / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D033921:Vesicular Transport Proteins / Q000037:antagonists & inhibitors
D015220:Calcium Channels; D033921:Vesicular Transport Proteins; D018698:Glutamic Acid; D011188:Potassium