HCO(-3)-dependent pHi recovery and overacidification induced by NH+4 pulse in rat lung alveolar type II cells: HCO(-3)-dependent NH3 excretion from lungs?
Intracellular pH (pHi) after the NH+4 pulse addition and its removal were measured in isolated alveolar type II cells (ATII cells) using BCECF fluorescence. In the absence of HCO(-3), the NH+4 pulse addition increased pHi (alkali jump) and its removal decreased pH(i) (acid jump) to the control level (no overacidification). This pHi change was induced by reaction 1 (NH3 + H+ <--> NH+4). However, in the presence of HCO(-3), the NH+4 pulse removal decreased pHi (acid jump) with overacidification. The extent of overacidification was decreased by acetazolamide (a carbonic anhydrase inhibitor), bumetanide (an inhibitor of Na+/K+/2Cl(-) cotransporter [NKCC]), and NPPB (an inhibitor of Cl(-) channel). The NH+4 pulse addition led to the accumulation of NH+4 in ATII cells via reaction 1 and NKCC, and the NH+4 pulse removal induced reaction 2 (NH+4 + HCO(-3) --> NH3 + H+ HCO(-3)) in addition to the reversal of reaction 1. Thus, NH+4 that entered via NKCC reacts with HCO(-3) (reaction 2) to produce H+, which induces overacidification in the acid jump. After the overacidification, the pH(i) recovery consisted of a rapid recovery (first phase) followed by a slow recovery (second phase). The first phase was inhibited by NPPB, glybenclamide, amiloride, and an Na+-free solution, and the second phase was inhibited by DIDS, MIA, and an Na+-free solution. Both phases were accelerated by a high extracellular HCO(-3) concentration. These observations indicate that the first phase was induced by HCO(-3) entry via Cl(-) channels coupled with Na+ channels activities, and that the second phase was induced by H+ extrusion via Na+/H+ exchanger and by HCO(-3) entry via HCO(-3) cotransporter. Thus, in ATII cells, HCO(-3) entry via Cl(-) channels is essential for recovering pHi after overacidification during the acid jump and for removing NH+4 that entered via NKCC from ATII cells, suggesting HCO(-3)-dependent NH3 excretion from lungs.
Tokuda
Sachiko
S
Central Research Laboratory Nakahari Project, Osaka Medical College, 2-7 Daigakucho, Takatsuki 569-8686, Japan.
Shimamoto
Chikao
C
Yoshida
Hideyo
H
Murao
Hitoshi
H
Kishima
Gen-ichi
G
Ito
Shigenori
S
Kubota
Takahiro
T
Hanafusa
Toshiaki
T
Sugimoto
Tohru
T
Niisato
Naomi
N
Marunaka
Yoshinori
Y
Nakahari
Takashi
T
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000187:drug effects / Q000378:metabolism; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D018942:Macrolides / Q000494:pharmacology; D008297:Male; D009579:Nitrobenzoates / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism
D001639:Bicarbonates; D018118:Chloride Channels; D004791:Enzyme Inhibitors; D018942:Macrolides; D009579:Nitrobenzoates; D000644:Quaternary Ammonium Compounds; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D002034:Bumetanide; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D000641:Ammonia; D000584:Amiloride; C036978:concanamycin A; D002256:Carbonic Anhydrases; D000086:Acetazolamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D005905:Glyburide