Aminophylline and theophylline derivatives as antagonists of neuronal depression by adenosine: a microiontophoretic study.

Aminophylline, theophylline, etamiphylline and diprophylline have been tested as antagonists of neuronal inhibition produced by microiontophoretically applied adenosine, when ejected as cations or anions. Aminophylline proved to be an effective adenosine antagonist when ejected as an anion, especially from alkaline solution. Anionic theophylline was also effective but less so, and on a smaller proportion of neurones. Ethylenediamine and hydroxyl ions had no effect on adenosine responses. GABA depressions were unaffected by any of the methylxanthines at the time of adenosine blockade. Cationic ejection from aminophylline or ethylenediamine barrels produced a depression of unit firing on about one third of the cells tested, but no antagonism of adenosine was observed. It is concluded that the anionic ejection of aminophylline from alkaline solution, or of etamiphylline of diprophylline, yields potentially useful antagonists of adenosine for iontophoretic experiments.