Ionic currents in crustacean neurosecretory cells.
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)
Onetti
C G
CG
Departamento de Fisiologia, Biofisica y Neurociencias, CINVESTAV, Mexico, D.F.
García
U
U
Valdiosera
R F
RF
Aréchiga
H
H
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D003400:Astacoidea / Q000378:metabolism*; D001369:Axons / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D007473:Ion Channels / Q000378:metabolism*; D008297:Male; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009490:Neurosecretory Systems / Q000166:cytology* / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
D007473:Ion Channels; D015221:Potassium Channels; D011189:Potassium Chloride; D012964:Sodium; D002118:Calcium