Effect of methuenine on the fast inward sodium current in frog atrial fibres

The effect of methuenine (a synthesized molecule derived from the ervatamine molecule ; a natural α acyl alkaloid) on action potential and fast inward Na current of frog atrial fibres was studied using the double sucrose gap technique. The drug 13 μM blocked the action potential without altering the resting membrane potential. Methuenine inhibited the fast Na conductance without changing the selectivity of the Na channel. The kinetic parameters of the Na current were not markedly shifted. The steady state inactivation curve was only slightly shifted towards more negative membrane potentials. The inhibition of the Na conductance by methuenine was frequency dependent. The data suggest that methuenine effect on Na current are slightly different from the effect of ervatamine. Methuenine might be effective in control of cardiac arrhythmias since the drug mainly decreased the excitability of depolarized fibres.