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Fading and rebound of P2X2 currents at millimolar ATP concentrations caused by low pH
1Geneva Biomedical Research Institute, Glaxo-Wellcome Research and Development, Geneva, Switzerland.
Abstract:
When ATP is applied at high concentrations (above 1 mM) to PC12 cells, it produces a rapidly desensitizing peak current followed by a rebound of the current after termination of the ATP application. We expressed P2X2 receptors, which are thought to mediate the ATP currents of PC12 cells, in HEK293 cells and studied the effects of acidification on this 'fading and rebound' phenomenon. We found that the desensitization disappeared after adjusting the low pH (<5.0) of the millimolar ATP concentrations to a more physiological value (pH 7.3). Furthermore, the fading and rebound could also be induced at much lower ATP concentrations by decreasing the pH of the ATP containing application solutions. Thus, it appears this phenomenon is not caused directly by high concentrations of ATP, but is due to a concomitant acidification that occurs when high concentrations of ATP are dissolved in only moderately buffered application solutions.
Insights
High concentrations of adenosine triphosphate (ATP) cause cell current changes due to solution acidification, not ATP levels alone. Lowering pH induces this
Area of Science:
- Cellular and Molecular Biology
- Neuroscience
- Biophysics
Background:
- PC12 cells exhibit a 'fading and rebound' current phenomenon when exposed to high adenosine triphosphate (ATP) concentrations.
- This phenomenon is characterized by rapid current desensitization followed by a rebound upon ATP removal.
Purpose of the Study:
- To investigate the role of acidification in the 'fading and rebound' phenomenon observed with high ATP concentrations in PC12 cells.
- To determine the effects of pH on P2X2 receptor-mediated currents.
Main Methods:
- Expression of P2X2 receptors in HEK293 cells.
- Application of millimolar ATP solutions at varying pH levels.
- Electrophysiological recording of cell currents.
Main Results:
- Desensitization of ATP-induced currents was abolished when low pH (<5.0) ATP solutions were adjusted to physiological pH (7.3).
- The 'fading and rebound' phenomenon could be induced at lower ATP concentrations by decreasing the pH of the application solution.
- Acidification, not high ATP concentration, appears to be the primary cause of the observed current desensitization and rebound.
Conclusions:
- The 'fading and rebound' phenomenon in PC12 cells is primarily driven by solution acidification associated with high ATP concentrations.
- P2X2 receptors are sensitive to pH changes, influencing their current response.
- This finding suggests that careful control of solution pH is crucial when studying ATP-mediated cellular responses.