Tetrodotoxin (TTX), a toxin from pufferfish, selectively blocks sodium channels in nerve and muscle cells, preventing action potential generation without affecting potassium channels. This study used the sucrose-gap voltage-clamp technique to examine sodium and potassium currents in lobster giant axons. TTX at concentrations of 1×10⁻⁷ to 5×10⁻⁹ gm/ml blocked action potentials but did not affect resting potential. Sodium conductance increased during depolarization, but this was suppressed by TTX, while potassium conductance remained unchanged. These findings support the hypothesis that TTX selectively inhibits sodium channels, preserving potassium function. The study also compared TTX with local anesthetics like cocaine and procaine, which block both sodium and potassium currents. TTX, however, only affects sodium channels, as evidenced by the selective suppression of sodium currents and the lack of change in potassium currents. TTX's effectiveness was observed even at low concentrations, with recovery possible after washing. The results indicate that TTX's action is reversible under appropriate conditions. The study further demonstrated that TTX selectively blocks the sodium-carrying mechanism, reducing the maximum rate of rise of the action potential without affecting the resting potential. This selective blockage is consistent with the idea that local anesthetics primarily affect the sodium channel mechanism rather than the resting potential mechanism. The findings suggest that TTX's action is highly selective, blocking sodium channels at very low concentrations (around 5×10⁻⁹ gm/ml). This selectivity is in contrast to other anesthetics, which have higher effective concentrations and affect both sodium and potassium channels. The study also highlights the importance of voltage-clamp experiments in understanding the mechanisms of ion channel blockage by toxins and anesthetics. The results contribute to the understanding of how local anesthetics and toxins affect nerve and muscle function, and provide insights into the molecular mechanisms underlying these effects.Tetrodotoxin (TTX), a toxin from pufferfish, selectively blocks sodium channels in nerve and muscle cells, preventing action potential generation without affecting potassium channels. This study used the sucrose-gap voltage-clamp technique to examine sodium and potassium currents in lobster giant axons. TTX at concentrations of 1×10⁻⁷ to 5×10⁻⁹ gm/ml blocked action potentials but did not affect resting potential. Sodium conductance increased during depolarization, but this was suppressed by TTX, while potassium conductance remained unchanged. These findings support the hypothesis that TTX selectively inhibits sodium channels, preserving potassium function. The study also compared TTX with local anesthetics like cocaine and procaine, which block both sodium and potassium currents. TTX, however, only affects sodium channels, as evidenced by the selective suppression of sodium currents and the lack of change in potassium currents. TTX's effectiveness was observed even at low concentrations, with recovery possible after washing. The results indicate that TTX's action is reversible under appropriate conditions. The study further demonstrated that TTX selectively blocks the sodium-carrying mechanism, reducing the maximum rate of rise of the action potential without affecting the resting potential. This selective blockage is consistent with the idea that local anesthetics primarily affect the sodium channel mechanism rather than the resting potential mechanism. The findings suggest that TTX's action is highly selective, blocking sodium channels at very low concentrations (around 5×10⁻⁹ gm/ml). This selectivity is in contrast to other anesthetics, which have higher effective concentrations and affect both sodium and potassium channels. The study also highlights the importance of voltage-clamp experiments in understanding the mechanisms of ion channel blockage by toxins and anesthetics. The results contribute to the understanding of how local anesthetics and toxins affect nerve and muscle function, and provide insights into the molecular mechanisms underlying these effects.