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P‐ERK Activation by Extracellular or Intracellular Acidosis Slows NHE3‐Mediated Acid Extrusion And Activates Ammoniagenesis in LLC‐PK1‐F+ Cells
Author(s) -
Oliver Robert Earl,
Kaur Primal,
Turturro Francesso,
Friday Ellen,
Welbourne Tomas
Publication year - 2007
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.21.6.a1414-c
Subject(s) - acidosis , extracellular , mapk/erk pathway , intracellular ph , intracellular , medicine , chemistry , endocrinology , kinase , biochemistry
We exposed proximal tubule‐like F + cells to extracellular acidosis pHo=6.8 or troglitazone (TRO)‐induced intracellular acidosis pHi<6.8(pHo=7.4) for 4min and 3h in order to determine cell signaling and physiological responses (NHE3 activity and NH 4 + production). Exposure to pHo =6.8 for 4min and 3h reduced the pHi from 7.32 ±0.07 to 6.96±0.04 and 6.75±0.11 associated with a 2.3 and 2.7 fold rise in PERK/T‐ERK ratio (both p<0.05). Exposure to TRO (20uM) reduced pHi from 7.32±0.07 to 6.60±0.08 and 6.86±0.15 associated with a 3.7 and 2.1 rise in P‐ERK at 4min and 3h respectively. NHE3 activity measured after transient 6min exposure to pHo=6.8 was reduced by 32% (p<0.01) while NH 4 + increased by 1.65 fold (p<0.05) at 3h; TRO reduced NHE3 activity by 82% and NH 4 + 2.4 fold (both p<0.01). TRO‐induced P‐ERK activation and fall in pHi was prevented by inhibiting EGFR in contrast EGFR inhibition with pHo 6.8 did not decrease P‐ERK activation or cellular acidosis. Pre‐incubation with MEKK inihibitors PD98059 and UO126 prevented the acidosis‐induced increase in P‐ERK and ammoniagenesis. Our results are consonant with P‐ERK activation associated with extracellular acidosis and intracellular acidosis (K + deficiency?) playing a major role in regulating acute physiological responses.