Related Experiment Video
Updated: Mar 11, 2026

Levator Auris Longus Preparation for Examination of Mammalian Neuromuscular Transmission Under Voltage Clamp Conditions
Published on: May 5, 2018
Effects of phenytoin on the cyclic nucleotide system in the motor nerve terminal
Abstract:
The effects of phenytoin on the motor nerve terminal were evaluated on the in vivo cat soleus nerve muscle preparation. Phenytoin, 10 mg/kg, reduced the repetitive aftercharges in motor nerve endings due to tetanic conditioning. It also reduced the repetitive activity due to adenylate cyclase activation with NaF, or to exogeneous dibutyryl cyclic AMP. These effects of phenytoin could be reversed by administering theophylline, a phosphodiesterase inhibitor, or by increasing the extracellular concentration of calcium. The effects of phenytoin could also be reversed by 3-aminopyridine, but not by tetraethylammonium chloride. Verapamil, a calcium current antagonist, produced effects that were identical to phenytoin. It is concluded that phenytoin blocks a cyclic nucleotide-mediated calcium influx that is associated with transmitter release. This calcium flux also appears to control a slow potassium current that is responsible for post-tetanic hyperpolarization.
Related Concept Videos
Neurochemical Transmission: Sites of Drug Action
Neuromuscular Junction And Blockade
Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open....
Ligand-Gated Ion Channel Receptor: Gating Mechanism
Excitatory and Inhibitory Effects of Neurotransmitters
Antiepileptic Drugs: Sodium Channel Blockers
Sodium channel blockers modulate ion channels, particularly voltage-gated sodium channels. They block only sodium ion movement.
Among the most commonly prescribed antiepileptic drugs are...

