Effect of Pinellia ternata lectin on membrane currents of mouse motor nerve terminals.

Pinellia ternata lectin (PTL) extracted from the fresh juice of rhizome of pinellia ternata used as a traditional Chinese medicine facilitated the quantal release of acetylcholine (ACh) in the mouse motor nerve terminals and formed cation channels in artificial lipid bilayer. Here we report the action of PTL on presynaptic membrane currents of motor nerve terminals. The experiments were performed on the intercostal nerve triangularis sterni muscle preparations. By means of the perineurial recording, the effects of PTL on the sodium current in the preterminal part, three potassium currents and two calcium currents generated from the nerve terminals were investigated. The results show that PTL increases voltage-dependent fast Ca2+ current (ICa.f), Na+ current (INa) and Ca(2+)-activated K+ current (IK,Ca) without action on either the voltage-dependent fast K+ current (IK,f) or the slow K+ current (IK,s). These effects are irreversible, but can be reversed by mannan, the specific binding sugar for PTL. The total action of PTL can be considered to raise [Ca2+]i by promoting Ca2+ influx, and then facilitate the neurotransmitter release. To our knowledge, this is the first report about the influence of lectin on presynaptic membrane currents at mammalian motor nerve terminals.