QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fieber, L. A. Search for Related Content PubMed PubMed Citation Articles by Fieber, L. A. Social Bookmarking                         What's this?

Journal of Experimental Biology, Vol 198, Issue 11 2337-2347, Copyright © 1995 by Company of Biologists

JOURNAL ARTICLES

Characterization and modulation of Na+ and Ca2+ currents underlying the action potential in bag cells of two species of Aplysia

LA Fieber
Division of Marine Biology and Fisheries, University of Miami Rosenstiel School of Marine and Atmospheric Science, FL 33149-1098, USA.

The neurosecretory bag cells of Aplysia produce long trains of action potentials (afterdischarge) to release hormones important to egg laying. These ionic currents are modulated by second messengers. Modulation of excitability in bag cells is incompletely understood partly because the currents that are modulated have not been fully characterized. Whole-cell voltage-clamp experiments were executed in cultured cells from sexually mature A. californica and A. brasiliana to characterize the inward voltage-gated currents for Na+ and Ca2+. These species had similar Na+ and Ca2+ current characteristics. The Na+ currents activated at voltages less negative than -30 mV and peaked at between +10 and +20 mV in artificial sea water. The time course and pharmacology of bag cell Na+ currents were similar to those of fast Na+ current in other excitable cells. Na+ currents were abolished in Na(+)-free extracellular solution and were not inhibited by Cd2+. The KD for inhibition by tetrodotoxin was 2.6 nmol l-1. The Na+ current was relatively insensitive to depolarized holding potentials (Vh), maintaining approximately 65% of peak current amplitude throughout the activation range at Vh = -30 mV. In experiments using a 1 s depolarized Vh prior to a test pulse, the half-inactivation voltage (V1/2) was -21 mV. The time constant of recovery from steady-state activation was 2.9 ms at Vh = -70 mV and 6.8 ms at Vh = -30 mV. The Ca2+ currents activated near -10 mV and peaked at approximately +20 mV with 11 mmol l-1 Ba2+ as the charge carrier. The pharmacology and V1/2 of bag cell Ca2+ current were similar to those of L-type Ca2+ currents. In extracellular solution without Na+, but containing Ba2+, Cs+ and tetraethylammonium, the Ca2+ current was inhibited by 25-100% by nifedipine (10 mumol l-1), mean 42%, and was unaffected in the majority of cells by omega-conotoxin (10 mumol l-1). The Ca2+ current was insensitive to Ni2+ (100 mumol l-1), but was abolished by 100 mumol l-1 Cd2+. Like the Na+ current, the Ca2+ current was relatively insensitive to depolarized Vh, maintaining more than 80% of peak current amplitude throughout the activation range at Vh = -40 mV. With a 1 s depolarized Vh prior to a test pulse, the V1/2 was -30 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				S. Michel and N. L. Wayne Neurohormone Secretion Persists after Post-Afterdischarge Membrane Depolarization and Cytosolic Calcium Elevation in Peptidergic Neurons in Intact Nervous Tissue J. Neurosci., October 15, 2002; 22(20): 9063 - 9069. [Abstract] [Full Text] [PDF]

				D. A. Baxter, C. C. Canavier, J. W. Clark Jr., and J. H. Byrne Computational Model of the Serotonergic Modulation of Sensory Neurons in Aplysia J Neurophysiol, December 1, 1999; 82(6): 2914 - 2935. [Abstract] [Full Text] [PDF]