Jm. Langosch et al., CHARACTERIZATION AND TRANSDUCTION MECHANISMS OF PURINOCEPTORS IN ACTIVATED RAT MICROGLIA, British Journal of Pharmacology, 113(1), 1994, pp. 29-34
1 Purinoceptor agonist-induced currents in untreated (proliferating) a
nd lipopolysaccharide- (LPS; 100 ng m(-1)) treated (nan-proliferating)
rat microglial cells were recorded by the whole-cell patch-clamp tech
nique. 2 In non-proliferating microglia, adenosine (0.01-100 mu M), 2-
methylthio ATP (3-3000 nM), ATP (0.1-1000 mu M), and ATP-gamma-S (1-10
mu M), but not alpha,beta-methylene ATP (alpha,beta-MeATP; 100 mu M)
produced a slow outward current at a holding potential of 0 mV. When K
+ was replaced in the pipette solution by an equimolar concentration o
f Cs+ (150 mM), the 2-methylthio ATP- (300 nM) induced outward current
disappeared. The effect of 2-methylthio ATP (300 nM) did not depend o
n the presence of extracellular Mg2+ (1 mM). The outward current respo
nse to 2-methylthio ATP (300 nM) was larger in proliferating than in n
on-proliferating microglia. 3 ATP (1-1000 mu M) evoked a fast inward c
urrent at a holding potential of - 70 mV in nonproliferating microglia
, while adenosine (100-1000 mu M) was inactive. When the effects of AT
P were compared at 0 and - 70 mV, it became evident that ATP is much m
ore potent in evoking the outward current. 4 The 2-methylthio ATP- (30
0 nM) induced outward current was blocked by suramin (300 mu M), but n
ot by 8-(p-sulphophenyl)-theophylline (100 mu M), while the adenosine-
(1 mu M) induced outward current had the reverse sensitivity to these
antagonists. 5 The 2-methylthio ATP- (300 nM) induced outward current
was inhibited by inclusion of GDP-beta-S (200 mu M) into the pipette
solution or by preincubation of microglial cells with pertussis toxin
(50 ng ml(-1)) for 12 h. The 2-methylthio ATP- (300 PM) induced inward
current was not changed by intracellular GDP-beta-S (200 mu M). The o
utward current response to adenosine (1 mu M) was also abolished after
pretreatment with pertussis toxin (50 ng ml(-1)). 6 Rat microglia pos
sess both ATP-sensitive P-2Y and adenosine-sensitive Pt-purinoceptors.
The ATP-evoked inward current is mediated by P-2Y-purinoceptors, whil
e the ATP- and adenosine-evoked outward currents are mediated by P-2Y-
and P-1-purinoceptors, respectively. The transduction mechanisms of t
he outward, but not the inward current activation involve a pertussis
toxin-sensitive G protein.