Intracellular acidification in neurons induced by ammonium depends on KCC2 function
Stefan Titz1, Sheriar Hormuzdi, Andrea Lewen
1Institut für Physiologie und Pathophysiologie und Interdisziplinäres Zentrum für Neurowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 326, 69120 Heidelberg, Germany.
The European Journal of Neuroscience
|January 20, 2006
Summary
The neuron-specific potassium-chloride cotransporter 2 (KCC2) is the primary route for neuronal ammonium (NH4+) uptake. Ammonium chloride-induced acid shifts indicate KCC2 function, crucial for understanding neuronal development and disease.
Area of Science:
- Neuroscience
- Cellular Physiology
- Ion Transport
Background:
- The KCC2 cotransporter mediates hyperpolarizing inhibition in neurons by extruding chloride ions.
- KCC2 has the capacity to transport ammonium (NH4+) instead of potassium (K+).
- The specific role of KCC2 in neuronal NH4+ uptake remains largely uncharacterized.
Purpose of the Study:
- To investigate the role of KCC2 in mediating NH4+ uptake in cultured rat brain neurons.
- To determine if KCC2 is the principal pathway for neuronal NH4+ influx.
- To establish NH4Cl-induced acid shifts as a functional indicator of KCC2 activity.
Main Methods:
- Cultured rat brain neurons were subjected to applications of ammonium chloride (NH4Cl).
- Intracellular pH changes were monitored using pH-sensitive indicators to detect acid shifts.
- The effects of pharmacological inhibitors (furosemide, bumetanide) and ionic conditions (Ba2+, Na+-free, extracellular K+) on NH4Cl-induced responses were assessed.
- GABA responses and associated calcium (Ca2+) changes were analyzed to correlate with KCC2 function.
Main Results:
- NH4Cl application induced rapid alkaline shifts followed by rebound acid shifts in mature neurons.
- Furosemide significantly blocked NH4Cl-induced rebound acid shifts, while bumetanide had minimal effect.
- Rebound acid shifts were inhibited by extracellular K+ but persisted in Ba2+ and Na+-free solutions.
- Neurons lacking functional KCC2 (depolarizing GABA responses) showed minimal NH4Cl-induced acidosis.
- Neurons with established KCC2 function (decreasing Ca2+ responses) exhibited significant rebound acid shifts.
Conclusions:
- KCC2 represents the major pathway for rapid neuronal NH4+ uptake.
- NH4Cl-induced rebound acid shifts serve as a reliable indicator of developing KCC2 function.
- The developmental upregulation of KCC2 facilitates significant NH4+ influx, with potential pathophysiological implications.
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