These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Characterization of Na+ and Ca2+ currents in bag cells of sexually immature Aplysia californica.
    Author: Fieber LA.
    Journal: J Exp Biol; 1998 Mar; 201(Pt 5):745-54. PubMed ID: 9542153.
    Abstract:
    The neurosecretory bag cells of sexually mature Aplysia californica release egg-laying hormones as part of the reproductive process after a train of action potentials termed afterdischarge. Whole-cell voltage-clamp experiments were performed in cultured cells from sexually immature A. californica to characterize the inward voltage-gated currents for Na+ and Ca2+. The goal of these experiments was to investigate the regulation of excitability during sexual maturation. Na+ currents in bag cells of immature A. californica were similar in several ways to those of mature animals. The Na+ currents activated at voltages less negative than -30 mV and peaked at 10-20 mV in artificial sea water. The time course and pharmacology of bag cell Na+ currents were similar to those of bag cells from mature A. californica, although the Na+ current density was lower in immature A. californica. Na+ currents were inhibited by tetrodotoxin (50 nmol l-1). The Na+ current was relatively insensitive to depolarized holding potentials (Vh), maintaining approximately 50% of peak current amplitude present at Vh = -70 mV 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 -27 mV. Recovery of immature Na+ current from steady-state inactivation at Vh = -30 mV had a time constant (tau) of 9.5 ms, significantly slower than in mature animals. Ca2+ currents of immature A. californica activated at approximately -30 mV and peaked at approximately 20 mV with 11 mmol l-1 Ba2+ as the charge carrier. The principle differences from mature Ca2+ currents were the low density of the immature Ca2+ currents and their 'run-down' in whole-cell recordings. The pharmacology and V1/2 of bag cell Ca2+ currents were similar to those of L-type Ca2+ currents in mature cells. The Ca2+ currents were inhibited 61 +/- 10% by nifedipine (10 mumol l-1) and were unaffected by omega-conotoxin GVIA (10 mumol l-1). The Ca2+ currents were relatively insensitive to depolarized Vh, activating maximally at Vh = -90, -70 and -50 mV, and maintaining 50% of this peak current amplitude throughout the activation range at Vh = -30 mV. The V1/2 was -23 mV in experiments in which cells were subjected to a 1 s depolarized Vh prior to a test pulse. Na+ current amplitudes were maintained or increased during 1 min of 4 Hz test pulses in bag cells at Vh = -70 mV and Vh = -30 mV. In contrast, Ca2+ current run-down occurred during 1 min of 4 Hz test pulses in seven of 10 cells at Vh = -70 mV and in 12 of 12 cells at Vh = -30 mV. The observed scarcity of Na+ and Ca2+ currents in immature bag cells as well as the specific characteristics of immature bag cell Ca2+ currents make repetitive action potential firing and hormone release less likely than in mature bag cells.
    [Abstract] [Full Text] [Related] [New Search]