Differential responses of synaptosomal cation movements and respiration to the convulsants penicillin, pentylenetetrazol and 3-aminopyridine.
The effect of three convulsants was tested in rat cortical synaptosomes by measuring Na+ and K+ movements and respiration. Penicillin (of its derivatives the 3-phenyl-5-methyl-4-isoxazolyl-penicillin, i.e. oxacillin was used) at 2 to 14 mM concentration prolonged the uptake phase of the K+-curve without altering final cation equilibrium. Pentylenetetrazol, at 10 to 50 mM exerted a concentration-dependent inhibitory effect on K+-uptake, while 3-aminopyridine was effective only at high concentrations (50 mM) preventing synaptosomal K+-uptake and increasing the synaptosomal Na+-content without, however, blocking respiration. The data suggest a transitional rise of K+-permeability of synaptosomal membrane in the presence of oxacillin, without lasting depolarization. Sufficient doses of 3-aminopyridine probably depolarize synaptosomes, the underlying mechanism probably being associated with the primary blocking of K+-channels and a subsequent increase in Na+ influx rather than with the inhibition of the Na+--K+-pump.
D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D002412:Cations / Q000378:metabolism*; D003292:Convulsants / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects; D010406:Penicillins / Q000494:pharmacology; D010433:Pentylenetetrazole / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012119:Respiration / Q000187:drug effects*; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism*
D000631:Aminopyridines; D002412:Cations; D003292:Convulsants; D010406:Penicillins; C031283:3-aminopyridine; D012964:Sodium; D011188:Potassium; D010433:Pentylenetetrazole