Vanillin modulates the fast outward and calcium currents in Helix neurons

A study was made to characterize the actions of vanillins on the resting membrane potential, action potential, membrane resistance and membrane ionic currents of identified Helix neurons. Two types of neurons can be classified according to the actions of vanillins. One type of neurons are the L and RPa 1-3 cells. Vanillin slightly depolarized these cells and moderately prolonged the action potential duration while increased the membrane resistance and initiated spontaneous spiking. Under voltage clamp, vanillin decreased the leak current, moderately suppressed the amplitude and decreased the time constant of decay of the A-currents in dose-dependent way (Kd = 5mM, nH = 0.6). The delayed outward currents were not influenced by vanillins. Vanillin decreased the plateau potential of the Ca-spike in Na-free TEA solution and decreased the peak Ca-currents under voltage clamp. Second type of neurons are some pacemaker cells around the RPa burster. Vanillin caused a burst-like transformation of the beating activity followed by slowly developing presynaptic activation. The most characteristic action of vanillins on these cells is a long-lasting enhancement of the Ca-currents under voltage clamp.