Role of cyclic ADP-ribose in ATP-activated potassium currents in alveolar macrophages.
There is growing evidence that extracellular ATP causes a dramatic change in the membrane conductance of a variety of inflammatory cells. In the present study, using the nystatin perforated patch recording configuration, we found that ATP (0.3-30 microM) induced a transient outward current in a concentration-dependent manner and that the reversal potential of the ATP-induced outward current was close to the K+ equilibrium potential, indicating that the membrane behaves like a K+ electrode in the presence of ATP. The first application of ATP to alveolar macrophages perfused with Ca2+-free external solution could induce the outward current, but the response to ATP was diminished with successive applications. Intracellular perfusion with a Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid, also diminished the response. When cyclic ADP-ribose (cADPR) was applied to the macrophage cytoplasm, a transient outward current was elicited. Thereafter, the successive outward current was inhibited, suggesting the involvement of cADPR in the response. Intracellular perfusion with inositol 1,4, 5-trisphosphate also induced a transient outward current, but the successive current was not inhibited. The ATP-induced outward current was abolished when 8-amino-cADPR (as a blocker of cADPR, 10(-6)-10(-5) M) was introduced into the cytoplasm. Homogenates of alveolar macrophages showed both ADP-ribosyl cyclase and cADPR hydrolase activities, and CD38 (ADP-ribosyl cyclase/cADPR hydrolase) expression was confirmed by reverse transcriptase-polymerase chain reaction and Western blot analyses. These results indicate that ATP activates K+ currents by releasing Ca2+ from cADPR-sensitive internal Ca2+ stores.
Ebihara
S
S
First Department of Internal Medicine, Tohoku University School of Medicine, Sendai 980-77, Japan.
Sasaki
T
T
Hida
W
W
Kikuchi
Y
Y
Oshiro
T
T
Shimura
S
S
Takasawa
S
S
Okamoto
H
H
Nishiyama
A
A
Akaike
N
N
Shirato
K
K
D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000008:administration & dosage / Q000378:metabolism*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D018999:Charybdotoxin / Q000494:pharmacology; D036563:Cyclic ADP-Ribose; D004305:Dose-Response Relationship, Drug; D016676:Macrophages, Alveolar / Q000378:metabolism*; D009761:Nystatin / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D011802:Quinidine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015290:Second Messenger Systems; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D018999:Charybdotoxin; D036563:Cyclic ADP-Ribose; D009761:Nystatin; D000246:Adenosine Diphosphate Ribose; D001030:Apamin; D019789:Tetraethylammonium; D000255:Adenosine Triphosphate; D011802:Quinidine; D002118:Calcium