Ionic currents in crustacean neurosecretory cells

Abstract

1. The patterns of electrical activity and membrane characteristics of a population of neurosecretory-cell somata in the X-organ of the crayfish were investigated with microelectrodes and whole-cell, voltage-clamp techniques. Some neurons (56%) were silent but could be excited by intracellular current injection: other cells showed spontaneous tonic activity (35%), and some had spontaneous bursting activity (9%). The spiking activity was abolished by tetrodotoxin (TTX) exposure and by severing the axon near the cell body. After axotomy, only a small, slow, regenerative depolarization remained that could be blocked by Cd2+. 2. Under voltage clamp the steady-state I-V curve in low [Ca2+]i (9 X 10(-9) M) showed a slope conductance of 16.7 +/- 3.9 (SD) nS (n = 10) at -50 mV and zero current potential of -50.1 +/- 7.7 mV. In current-clamp mode these neurons were either silent or fired tonically. With high [Ca2+]i (1.7 X 10(-6) M) both the slope conductance and inward and outward currents were reduced. In some neurons high [Ca2+]i reveals a negative slope resistance in the range of -46 to -41 mV. It could be supressed by removing [Na+]o, but it was TTX insensitive. These are the neurons that under current clamp showed bursting activity. 3. The main inward current in cell somata was a Ca2+ current of 2 +/- 0.6 nA (n = 18), activated at -40 mV and peaking at 20 mV. It showed relaxation with prolonged pulses. No Na(+)-dependent, TTX-sensitive inward currents were recorded with short (100-ms) pulses in axotomized neurons. 4. Two outward currents could be distinguished.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine nucleotides and intracellular Ca2+ regulate a voltage-dependent and glucose-sensitive potassium channel in neurosecretory cells

“…We would like to emphasize that in the presence of a quasi-physiological K + gradient, the KATP channels can be activated at membrane potential values ( Fig. 3A) close to the resting potential measured (-64 + 8 mV) in XO neurons [21]. Therefore, it is reasonable to propose that the current flowing through these channels contributes to the maintenance of the resting potential in these neurons.…”

“…The e-fold increase in Po (k = 18 mV) did not change significantly. Since the resting membrane potential of XO neurons is -64 + 8 mV[21], these results suggest that the glucose-sensitive channel can be activated at the membrane's resting potential.Voltage dependence of single-channel kinetics Single-channel kinetics were studied using open and closed dwell time histograms from four membrane patches that showed individual openings, interpreted as the activity of only a single channel at symmetrical concentrations of K § By fitting dwell time histograms to exponential functions, we obtained open and closed time constants at different membrane potentials. At all the membrane potentials tested, the open times were well described by single exponential functions, while closed times were described by two distinguishable exponential components of shorter and longer duration.…”

“…Single-channel current recordings were performed using cell-attached and inside-out patch configurations of the patch-clamp technique [10]. Membrane currents for perforated and cell-free patch-clamp experiments were recorded using a laboratory-made patch-clamp amplifier [21] with 100 Mf~ or 10 G~ feedback resistance in the current-voltage converter; the resistance of patch pipettes was 2 4 or 8 10 M~2. Patch pipettes were made from borosilicate capillary glass (1.5 mm OD, 0.86 mm ID; Sutter Instruments Novato, Calif., USA).…”

“…Neuronal cell bodies from the X organ (XO) have been studied with electrophysiological techniques; the ionic currents underlying the diversity of action potential firing patterns displayed by these neurosecretory cells have been characterized elsewhere [21]. Two voltage-dependent K + currents were described, and their importance in determining the firing rate and the shape of action potentials was pointed out [17].…”

Histamine operates Cl–-gated channels in crayfish neurosecretory cells

“…The method for isolating the eyestalk and intracellular recording was as described previously (Onetti et al, 1990). To obtain neuronal cultures, the animals were deeply anesthetized by burying them in triturate ice for 20·min, then the eyestalks were excised and placed in chilled crayfish saline solution, consisting of (in mmol·l -1 ): 205 NaCl, 5.4 KCl, 2.6 MgCl 2 , 13.5 CaCl 2 and 10 Hepes adjusted to pH·7.4 with NaOH.…”