Egg-laying hormone of Aplysia induces a voltage-dependent slow inward current carried by Na+ in an identified motoneuron.

Publisher Website
Google Scholar
Abstract
This report presents studies on ionic currents in Aplysia motoneuron B16 that are modulated by the neuropeptide egg-laying hormone (ELH) of Aplysia californica. ELH induces an inward current that persists in the presence of the peptide and that decays slowly after ELH is removed from the bath. The effect is not due to a decrease in the delayed potassium current, the calcium-activated potassium current, or the transient potassium current. Current-voltage measurements indicate that ELH produces increased inward currents from -8- mV to .apprxeq. 0 mV. The effect is particularly enhanced in the region from -40 mV to -25 mV where a negative slope conductance due to a voltage-dependent slow inward current is observed. The slow inward current and the response to ELH persist in saline solutions in which Ca2+ is replaced with Co2+ but are eliminated when Na2+ is replaced with equimolar concentrations of either Tris or N-methyl-D-glucamine. The response to ELH is unaffected by replacing chloride with equimolar acetate; by increasing the potassium concentration; or by adding tetraethylammonium chloride, CsCl, 4-aminopyridine, or tetrodotoxin to the saline bath. In addition, the reversal potentials for the ELH response (range, -28 to +46 mV), obtained from difference current-voltage relationships, are consistent with an increase in the Na+-dependent slow inward current. We conclude that at least one of the effects of ELH on B16 is to increase a slow inward current carried by Na+.