Ionic currents of morphologically distinct peptidergic neurons in defined culture

Abstract

1. The X-organ sinus gland is a major peptidergic neurosecretory system in Crustacea, analogous to the vertebrate hypothalamoneurohypophyseal system. Neuronal somata isolated from the crab (Cardisoma carnifex) X-organ and maintained in primary culture in unconditioned, fully defined medium show immediate regenerative outgrowth. Outgrowth occurring as broad lamellipodia ("veiled") distinguishes neurons consistently showing crustacean hyperglycemic hormone immunoreactivity. Neurons that are immunoreactive against molt-inhibiting hormone and red pigment concentrating hormone antisera give rise to branched neurites ("branched"). 2. The whole-cell variation of the patch-clamp technique was used to study the electrophysiology of these two cell types 24-48 h after plating. Under current clamp, only veiled neurons fired overshooting action potentials either spontaneously or in response to depolarization. 3. Under voltage clamp, net current was predominantly outward. When solutions that suppressed outward current were used, only veiled neurons showed significant inward current. These included a tetrodotoxin (TTX)-sensitive Na current and a slow (time to peak 6-10 ms at 0 mV) Cd-sensitive Ca current (ICa) that was activated at potentials less than -30 mV, was maximal at 0 to +20 mV, and did not reverse at potentials up to +60 mV. 4. In TTX, the form of the Ca current I(V) curve was unchanged by changes of holding potential between -40 and -80 mV, and 75-100% of ICa was available from -40 mV. 5. ICa inactivated slowly and incompletely. Analysis with two-pulse regimes suggested that both inactivation and facilitation mechanisms were present. 6. Outward current was examined in the presence and absence of 0.5 mM Cd2+ (1 microM TTX was always present in the external medium). Cd2+ ions slightly reduced the peak outward current, usually by less than 10% (Vc = -10 to +20 mV; Vh = -80 mV). All additional observations were in the presence of TTX and Cd2+. 7. Both cell types expressed a 4-aminopyridine (4-AP)-sensitive transient current, analogous to IA, and a slower-rising (minimum time to peak 20 ms), sustained current that was partially sensitive to tetraethylammonium, analogous to IK. 8. The mean Vh at which IA was half inactivated was -46 mV, and the mean time constant for removal of inactivation was 46 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

4‐aminopyridine activates potassium currents by activation of a muscarinic receptor in feline atrial myocytes.

“…To our knowledge, this is the first report of 4-AP increasing a potassium current in a cardiac preparation. In cultured peptidergic neurons from the X-organ of the crab, Meyers, Graf & Cooke (1992) found that 4-AP increased IK. They suggested that the blockade of IA in distal neurites improved voltage control and recruited additional conductance from distal regions of the membrane.…”

Effects of perfluorooctane sulfonate on ion channels and glutamate-activated current in cultured rat hippocampal neurons

“…Outward potassium currents of neurons were examined with a bath saline containing both TTX and Cd 2+ to eliminate possible competing inward Na + and Ca 2+ currents (Meyers et al, 1992;Richmond et al, 1995). Two subtypes of K + currents, transient outward current (I A ) and delayed rectifier current (I K ), were recorded with a series graded concentrations of PFOS applications.…”

The Crustacean Neuropeptides of the CHH/MIH/GIH Family: Structures and Biological Activities

“…Dispersed XO cells have been cultured in vitro, where they show axonal outgrowth and the development of elaborate branching and lamellipodial morphologies. Electrophysiological and morphological studies (e.g., on neurosecretory granule content) have been performed on such cells in culture (Cooke et al 1989;Grau and Cooke 1992;Meyers et al 1992), and LG lamina ganglionaris ; ME, MI, MT medullae externa, interna, and terminalis; SG sinus gland; XO X-organ. Bars b, c 50 urn; inset 10 urn.…”