title: Effects of harmaline on membrane excitability and ATPase activity of the crayfish giant axon.
abstract: Effects of harmaline on excitability of crayfish giant axon in relation to effects on Na,K-ATP activity were investigated and the findings were compared with relative data on ouabain. Exposure of the axon to harmaline in doses over 0.5 mM resulted in a dose-dependent reduction of the action potential. Harmaline of 2.5 mM produced a complete blockade of the action potential with a slight decrease in the resting membrane potential (5.7 mV), but no alterations of Na,K-ATPase activity. In contrast, ouabain (5 mM) produced a more pronounced decrease in the resting membrane potential (10.6 mV) and also a partial reduction in the action potential, while a significant decrease in Na,K-ATPase activity was obtained. Increasing the membrane potential to the initial level resulted in a partial recovery (46%) of the rising rate (dV/dt) of action potential. The dV/dt was exponentially decreased when the resting potential was reduced with application of KCl solution over 8 mV. These results suggest that harmaline externally applied produces a decrease in sodium conductance without affecting Na,K-ATPase activity, while ouabain inhibits Na,K-ATPase activity and, to lesser extent, decreases in sodium conductance.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000201:enzymology* / Q000378:metabolism; D017301:Ca(2+) Mg(2+)-ATPase; D004594:Electrophysiology; D006246:Harmaline / Q000494:pharmacology*; D066298:In Vitro Techniques; D008566:Membranes / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D000470:Alkaloids; D010042:Ouabain; D006246:Harmaline; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase