Potassium Currents in Isolated Statocyst Neurons and RPeD1 in the Pond Snail,Lymnaea stagnalis

Abstract

To begin to determine the underlying neural mechanisms of memory formation, we studied two different cell types that play important roles in different forms of associative learning in Lymnaea. Statocyst neurons (hair cells) mediate classical conditioning, whereas RPeD1 is a site of memory formation induced by operant conditioning of aerial respiration. Because potassium (K(+)) channels play a critical role in neuronal excitability, we initiated studies on these channels in the aforementioned neurons. Three distinct K(+) currents are expressed in the soma of both the hair cells and RPeD1. In hair cells and RPeD1, there is a fast activating and rapidly inactivating 4-aminopyridine (4-AP)-sensitive A current (I(A)), a tetraethyl ammonium (TEA)-sensitive delayed rectifying current, which exhibits slow inactivation kinetics (I(KV)), and a TEA- and 4-AP-insensitive Ca(2+)-dependent current (I(Ca-K)). In hair cells, the activation voltage of I(A); its half-maximal steady-state activation voltage and its half-maximal steady-state inactivation were at more depolarized levels than in RPeD1. The time constant of recovery from I(A) inactivation was slightly faster in hair cells. I(A) in hair cells is also smaller in amplitude than in RPeD1 and is activated at more depolarized potentials. In like manner, I(KV) is smaller in hair cells and is activated at more depolarized potentials than in RPeD1.

The fruit essential oil of Pimpinella anisum L. (Umblliferae) induces neuronal hyperexcitability in snail partly through attenuation of after-hyperpolarization

“…Based on current clamp condition we found that Pimpinella anisum essential oil led to a decrease in the amplitude of AHPs. In snail neurons, spike repolarization and AHP are determined by a set of potassium channels which underlie fast and delayed K + outward currents (Thompson, 1977;Solntseva, 1995;Bal et al, 2000Bal et al, , 2001Sakakibara et al, 2005), and also two classes of Ca 2+ activated K + channels; large conductance Ca 2+ activated K + channels (BK channels) and small conductance Ca 2+ activated K + channels (SK channels) (Hermann and Erxleben, 1987;Gola et al, 1990;Crest and Gola, 1993). In many neurons, Ca 2+ influx through voltage dependent Ca 2+ channels and consequent activation of Ca 2+ dependent potassium channels is a major determinant of AHP amplitude and duration.…”

Dopamine suppresses neuronal activity of Helisoma B5 neurons via a D2-like receptor, activating PLC and K channels

“…Studies in Lymnaea indicated the presence of two types of pharmacologically distinct K channels: one sensitive to TEA and the other to 4AP. They have been shown to contribute to different phases of action potential repolarization (Sakakibara et al, 2005). The perfusion of a cocktail of 20 mM TEA and 5 mM 4AP, concentrations that have been suggested to be effective to block both K channels in Helisoma and Lymnaea (Berdan and Easaw, 1992;Staras et al, 2002), caused a decrease in firing frequency by 34.5 ± 2.7% (n = 7, P < 0.05) combined with an increase in action potential amplitude by 21.5 ± 0.3% (n = 7, P < 0.05) (Fig.…”

Clinical dose of lidocaine destroys the cell membrane and induces both necrosis and apoptosis in an identified Lymnaea neuron

“…Whole-cell patch-clamp recordings in the Lymnaea neuron were made using a multiclamp 700 A amplifier (Axon Instruments) [26,27]. Patch electrodes (tip diameter adjusted to 1.0 lm; resistance, 1-3 MX) were pulled from glass tubing (outside diameter, 1.5 mm) with no filament (PG-150T-7.5; Warner Instrument, Hamden, CT, USA) on a vertical pipette puller (PA-10; Narishige, Tokyo, Japan).…”