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Upregulation of the hyperpolarization‐activated cation current in rat thalamic relay neurones by acetazolamide
Author(s) -
Munsch Thomas,
Pape HansChristian
Publication year - 1999
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 - 10.1111/j.1469-7793.1999.0505m.x
Subject(s) - acetazolamide , intracellular ph , chemistry , hyperpolarization (physics) , biophysics , intracellular , carbonic anhydrase , axolemma , bursting , electrophysiology , hepes , membrane potential , carbonic anhydrase inhibitor , biochemistry , neuroscience , medicine , stereochemistry , central nervous system , enzyme , biology , myelin , nuclear magnetic resonance spectroscopy
1 The effect of inhibition of brain carbonic anhydrase (CA) on the hyperpolarization‐activated cation current ( I h ) of thalamocortical (TC) neurones of the rat ventrobasal thalamic complex (VB) was investigated in an in vitro slice preparation using the whole‐cell patch‐clamp technique and fluorescence ratio imaging of the pH indicator 2′,7′‐bis(carboxyethyl)‐5(and ‐6)‐carboxyfluorescein (BCECF). 2 Recording of I h before and after addition of 0.4‐0.8 mM acetazolamide to the bathing fluid revealed a significant shift in the voltage dependence of activation (V ½ ) of 5‐7 mV to more positive potentials. 3 Simultaneous recording of I h and BCECF fluorescence ratio ( F 420 / F 495 ) revealed an increase in I h amplitude accompanied by an intracellular alkalinization upon application of acetazolamide. The CA inhibitor ethoxyzolamide (EZA, 50 μ m ) also led to an intracellular alkalinization and a subsequent 4‐5 mV positive shift of V ½ of I h . 4 Acetazolamide and EZA both profoundly slowed the rapid fall of pH i upon switching from Hepes‐ to CO 2 /HCO 3 − ‐buffered superfusate, indicating intracellular CA isoforms in TC neurones. 5 In slices bathed in Hepes‐buffered saline, addition of acetazolamide had no effect on the amplitude and time course of activation of I h , indicating that the action of acetazolamide on I h was dependent on the presence of HCO 3 − . 6 Under current‐clamp conditions, the neuronal response to hyperpolarizing current pulses in the presence of acetazolamide was decreased as compared to control. This resulted in a strongly reduced ability of TC neurones to produce rebound Ca 2+ ‐mediated spikes. 7 The present results implied that in TC neurones acetazolamide led to an intracellular alkalinization which causes, due to its pH sensitivity, an increase in I h .