In:
Journal of Neurophysiology, American Physiological Society, Vol. 87, No. 5 ( 2002-05-01), p. 2209-2224
Abstract:
The effects of anoxia on intracellular pH (pH i ) were examined in acutely isolated adult rat hippocampal CA1 neurons loaded with the H + -sensitive fluorophore, 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein. During perfusion with HCO[Formula: see text]/CO 2 - or HEPES-buffered media (pH 7.35) at 37°C, 5- or 10-min anoxic insults were typified by an intracellular acidification on the induction of anoxia, a subsequent rise in pH i in the continued absence of O 2 , and a further internal alkalinization on the return to normoxia. The steady-state pH i changes were not consequent on changes in [Ca 2+ ] i and, examined in the presence of HCO[Formula: see text], were not significantly affected by (DIDS). In the absence of HCO[Formula: see text] , the magnitude of the postanoxic alkalinization was attenuated when external Na + was reduced by substitution with N-methyl-d-glucamine (NMDG + ), but not Li + , suggesting that increased Na + /H + exchange activity contributes to this phase of the pH i response. In contrast, 100–500 μM Zn 2+ , a known blocker of H + -conductive pathways, reduced the magnitudes of the internal alkalinizations that occurred both during and following anoxia. The effects of NMDG + -substituted medium and Zn 2+ to reduce the increase in pH i that occurred after anoxia were additive. Consistent with the steady-state pH i changes, rates of pH i recovery from internal acid loads imposed immediately after anoxia were increased, and the application of Zn 2+ and/or perfusion with NMDG + -substituted medium slowed pH i recovery. Reducing extracellular pH from 7.35 to 6.60, or reducing ambient temperature from 37°C to room temperature, also attenuated the increases in steady-state pH i observed during and after anoxia and reduced rates of pH i recovery from acid loads imposed in the immediate postanoxic period. Finally, inhibition of the cAMP/protein kinase A second-messenger system reduced the magnitude of the rise in pH i after anoxia in a manner that was dependent on external Na + ; conversely, activation of the system with isoproterenol increased the postanoxic alkalinization, an effect that was attenuated by pretreatment with propranolol, Rp-cAMPS, or when NMDG + (but not Li + ) was employed as an external Na + substitute. The results suggest that a Zn 2+ -sensitive acid efflux mechanism, possibly a H + -conductive pathway activated by membrane depolarization, contributes to the internal alkalinization observed during anoxia in adult rat CA1 neurons. The rise in pH i after anoxia reflects acid extrusion via the H + -conductive pathway and also Na + /H + exchange, activation of the latter being mediated, at least in part, through a cAMP-dependent signaling pathway.
Type of Medium:
Online Resource
ISSN:
0022-3077
,
1522-1598
DOI:
10.1152/jn.2002.87.5.2209
RVK:
XA 10000 ; XA 552555
Language:
English
Publisher:
American Physiological Society
Publication Date:
2002
detail.hit.zdb_id:
80161-6
detail.hit.zdb_id:
1467889-5
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