Effects of ATP and elevated K+ on K+ currents and intracellular Ca2+ in human microglia.
We have used whole-cell patch-clamp recordings and calcium microfluorescence measurements to study the effects of ATP and elevated external K+ on properties of human microglia. The application of ATP (at 0.1 mM) led to the activation of a transient inward non-selective cationic current at a cell holding potential of -60 mV and a delayed, transient expression of an outward K+ current activated with depolarizing steps applied from holding level. The ATP response included an increase in inward K+ conductance and a depolarizing shift in reversal potential as determined using a voltage ramp waveform applied from -120 to -50 mV. Fura-2 microspectrofluorescence measurements showed intracellular calcium to be increased following the application of ATP. This response was characterized by an initial transient phase, which persisted in Ca2+-free media and was due to release of Ca2+ from intracellular storage sites. The response had a later plateau phase, consistent with Ca2+ influx. In addition, ATP-induced changes in intracellular Ca2+ exhibited prominent desensitization. Elevated external K+ (at 40 mM) increased inward K+ conductance and shifted the reversal potential in the depolarizing direction, with no effect on outward K+ current or the level of internal Ca2+. The results of these experiments show the differential responses of human microglia to ATP and elevated K+, two putative factors associated with neuronal damage in the central nervous system.
McLarnon
J G
JG
Department of Pharmacology and Therapeutics, Faculty of Medicine, The University of British Columbia, Vancouver, Canada.
Zhang
L
L
Goghari
V
V
Lee
Y B
YB
Walz
W
W
Krieger
C
C
Kim
S U
SU
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003592:Cytophotometry; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D017628:Microglia / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D012604:Scorpion Venoms
D005456:Fluorescent Dyes; D009498:Neurotoxins; D015221:Potassium Channels; D012604:Scorpion Venoms; C077910:margatoxin; D000255:Adenosine Triphosphate; D011188:Potassium; D002118:Calcium; D016257:Fura-2