Persistent Ca²⁺Current Contributes to a Prolonged Depolarization inAplysiaBag Cell Neurons

Abstract

Neurons may initiate behavior or store information by translating prior activity into a lengthy change in excitability. For example, brief input to the bag cell neurons of Aplysia results in an approximate 30-min afterdischarge that induces reproduction. Similarly, momentary stimulation of cultured bag cells neurons evokes a prolonged depolarization lasting many minutes. Contributing to this is a voltage-independent cation current activated by Ca(2+) entering during the stimulus. However, the cation current is relatively short-lived, and we hypothesized that a second, voltage-dependent persistent current sustains the prolonged depolarization. In bag cell neurons, the inward voltage-dependent current is carried by Ca(2+); thus we tested for persistent Ca(2+) current in primary culture under voltage clamp. The observed current activated between -40 and -50 mV exhibited a very slow decay, presented a similar magnitude regardless of stimulus duration (10-60 s), and, like the rapid Ca(2+) current, was enhanced when Ba(2+) was the permeant ion. The rapid and persistent Ca(2+) current, but not the cation current, were Ni(2+) sensitive. Consistent with the persistent current contributing to the response, Ni(2+) reduced the amplitude of a prolonged depolarization evoked under current clamp. Finally, protein kinase C activation enhanced the rapid and persistent Ca(2+) current as well as increased the prolonged depolarization when elicited by an action potential-independent stimulus. Thus the prolonged depolarization arises from Ca(2+) influx triggering a cation current, followed by voltage-dependent activation of a persistent Ca(2+) current and is subject to modulation. Such synergy between currents may represent a common means of achieving activity-dependent changes to excitability.

Diacylglycerol‐mediated regulation of Aplysia bag cell neuron excitability requires protein kinase C

“…; Tam et al . ; Groten & Magoski, ). Voltage‐gated currents were elicited by 200 ms voltage steps in 10 mV increments from −60 to +40 mV in neurons bathed in Ca 2+ ‐Cs + ‐TEA‐ASW and dialysed with Cs + ‐Asp‐based intracellular saline.…”

A potentially novel nicotinic receptor inAplysianeuroendocrine cells

“…1F), with 6 neurons firing action potentials. Considering that a strong depolarization will provoke voltage-gated Ca 2ϩ influx and potentially activate nonselective cation channels (Gardam and Magoski 2009;Hung and Magoski 2007;Lupinsky and Magoski 2006;Tam et al 2009), it was not surprising to find that three of the neurons reached a new steady state of Ϫ53.6 Ϯ 1.5 mV. On the other hand, a 2-s pressure application of 3 mM nicotine stimulated the neurons much less, with an average depolarization of ϳ18 mV (n ϭ 15) that was significantly different from depolarization by acetylcholine (Fig.…”

“…Thus, if there is an endogenous agonist for the nicotinic receptor, it may be a peptide, perhaps related to certain bungarotoxin-like peptides (Tsetlin 1999), or a metabolite (Grando 2008;Yassin et al 2001). Because the putative nicotine receptor is Ca 2ϩ permeable, it would allow for Ca 2ϩ influx at voltages nearer to the resting membrane potential than that permitted by voltage-gated Ca 2ϩ channels (Tam et al 2009). For example, ␣7-receptors produce Ca 2ϩ transients in dendritic spines, whereas ␣3-containing receptors augment global Ca 2ϩ increases through Ca 2ϩ -induced Ca 2ϩ -release (Shoop et al 2001).…”

Isolation of Sensory Neurons of <em>Aplysia californica</em> for Patch Clamp Recordings of Glutamatergic Currents

“…Long term cocultures also lend themselves to biochemical studies on single neurons. Success of the co-culture preparation is often attributed to the addition of up to 50% Aplysia hemolymph to cultures 17 . However, the success of this approach often depends on batch-to-batch variability of this hemolymph.…”