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期刊论文
Intracellular Calcium Transients and Potassium Current Oscillations Evoked by Glutamate in Cultured Rat Astrocytes
The Journal of Neuroscience, October 1, 1997, 17 (19): 7278-7287,-0001,():
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 ([Ca 2+]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 Ca21-stores by the Ca21-ATPase inhibitor cyclopiaconic acid (10μM). They reversed near -85 mV and were reduced by tetraethylammonium (10mM), 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.
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