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ERK Activation Regulates Acid Base Balance in Proximal Tubule‐like LLC‐PK1 Cells
Author(s) -
Oliver Robert E.,
Friday Ellen,
Turturro Francesco,
Welbourne Tomas
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.760.3
Subject(s) - mapk/erk pathway , chemistry , extracellular , acidosis , medicine , endocrinology , biochemistry , kinase
Both metabolic acidosis and glitazones (rosiglitazone, RGZ, and troglitazone, TRO) activate ERK in LLC‐PK1 cells. To determine the effect of p‐ERK on acid base balance without the complication of an extracellular acidosis, TRO was used to elevate p‐ERK with acid extrusion and total production monitored over a 12min time course. After 12min, the p‐ERK to total ERK ratio increased (p<0.01) 4.8fold (0.7± 0.2 to3.35±0.7) while the spontaneous pHi dropped (7.10±0.02 to 6.78±0.04, p<0.001). NHE3 activity assayed at the end of the 12min by acid (NH 4 + ) pulsing was reduced by 54% with the recovery pHi less (p<0.01) than the control recovery pHi (6.67± 0.07 vs. 7.04± 0.05). Activation of p‐ERK was associated with a 2fold increase (p<0.001) in acid production (402±34 vs. 207± 37nmol/12min) despite the fall in lactate released to the media with ERK activation (38 ± 3 vs. 57± 6nmol/12min, p<0.05). EIPA (100uM) reduced NHE3 activity by 63% but reduced pHi only minimally and failed to activate ERK or enhance acid production. Replacing glucose with 2‐deoyglucose abrogated the cellular acidosis (6.94± 0.03 vs. 6.71± 0.02, p<0.02) and prevented enhanced acid production (187± 9 vs. 423± 17nmoles/12min, p<0.001) with TRO but did not prevent the ERK activation. MEKK inhibitors PD98059 (30uM)+UO126 (10uM) completely prevented TRO‐induced ERK activation (0.3± 0.2 vs. 3.35± 1.1, p<0.01) and the fall in spontaneous pHi (7.02±0.03 vs. 6.78±0.04, p<0.001); total acid production and NHE3 activity in the presence of TRO returned to the control levels. RGZ gave similar effects but was less potent than TRO. These results are consonant with ERK activation playing a key role in PT cell acid base balance through regulation of both acid production and extrusion and suggest that the former may modulate extrusion.