Intracellular calcium transients and potassium current oscillations evoked by glutamate in cultured rat astrocytes.
Glutamate responses in cultured rat astrocytes from cerebella of neonatal rats were investigated using the perforated-patch configuration to record membrane currents without rundown of intracellular messenger cascades, and microfluorometric measurements to measure the intracellular Ca2+ concentration ([Ca2+]i) and intracellular pH (pHi) with fura-2 AM and 2',7'-bis-(2-carboxyethyl)-5,6-carboxyfluorescein acetoxy methylester respectively. In the perforated-patch mode, glutamate evoked single or multiple outward current transients in 82% of the cells, which disappeared when the recording technique was converted into a conventional whole-cell mode. The outward current transients were accompanied by [Ca2+]i transients, whereas pHi fell monophasically, without any sign of oscillation. Pharmacological analysis of the glutamate-induced responses indicated that ionotropic receptor activation evoked an inward current but no outward current transients, and metabotropic receptor activation (of the mGluR1/5 type) elicited outward current transients but no inward current. The outward current transients were reduced in frequency, or even abolished, after depletion of the intracellular Ca2+-stores by the Ca2+-ATPase inhibitor cyclopiaconic acid (10 microM). They reversed near -85 mV and were reduced by tetraethylammonium (10 mM), suggesting that they were caused by K+ channel activation. It is concluded that glutamate evoked these K+ outward current transients by oscillatory Ca2+ release mediated by mGluR activation. The corresponding membrane potential waves across the astroglial syncytium could provide spatial and temporal dynamics to the glial K+ uptake capacity and other voltage-dependent processes.
Chen
J
J
Abteilung für Allgemeine Zoologie, FB Biologie, Universität Kaiserslautern, D-67653 Kaiserslautern, Germany.
Backus
K H
KH
Deitmer
J W
JW
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D001692:Biological Transport; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D018698:Glutamic Acid / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism*; D008024:Ligands; D009991:Oscillometry; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017470:Receptors, Glutamate / Q000378:metabolism
D008024:Ligands; D017470:Receptors, Glutamate; D018698:Glutamic Acid; D011188:Potassium; D002118:Calcium