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Role of intracellular and extracellular pH in the chemosensitive response of rat locus coeruleus neurones
Author(s) -
Filosa J. A.,
Dean J. B.,
Putnam R. W.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.014142
Subject(s) - intracellular ph , chemistry , acidosis , extracellular , hepes , biophysics , alkalosis , hypercapnia , intracellular , ph meter , chromatography , biochemistry , biology , endocrinology
The chemosensitive response of locus coeruleus (LC) neurones to changes in intracellular pH (pH i ), extracellular pH (pH o ) and molecular CO 2 were investigated using neonatal rat brainstem slices. A new technique was developed that involves the use of perforated patch recordings in combination with fluorescence imaging microscopy to simultaneously measure pH i and membrane potential ( V m ). Hypercapnic acidosis (15 % CO 2 , pH o 6.8) resulted in a maintained fall in pH i of 0.31 pH units and a 93 % increase in the firing rate of LC neurones. On the other hand, isohydric hypercapnia (15 % CO 2 , 77 m m HCO 3 − , pH o 7.45) resulted in a smaller and transient fall in pH i of about 0.17 pH units and an increase in firing rate of 76 %. Acidified Hepes ( N ‐2‐hydroxyethylpiperazine‐ N ′‐2‐ ethanesulfonic acid)‐buffered medium (pH o 6.8) resulted in a progressive fall in pH i of over 0.43 pH units and an increase in firing rate of 126 %. Isosmotic addition of 50 m m propionate to the standard HCO 3 − ‐buffered medium (5 % CO 2 , 26 m m HCO 3 − , pH o 7.45) resulted in a transient fall in pH i of 0.18 pH units but little increase in firing rate. Isocapnic acidosis (5 % CO 2 , 7 m m HCO 3 − , pH o 6.8) resulted in a slow intracellular acidification to a maximum fall of about 0.26 pH units and a 72 % increase in firing rate. For all treatments, the changes in pH i preceded or occurred simultaneously with the changes in firing rate and were considerably slower than the changes in pH o . In conclusion, an increased firing rate of LC neurones in response to acid challenges was best correlated with the magnitude and the rate of fall in pH i , indicating that a decrease in pH i is a major part of the intracellular signalling pathway that transduces an acid challenge into an increased firing rate in LC neurones.