ISSN:
1573-6830
Keywords:
Aplysia neuron
;
calcium channel
;
barium current
;
pentobarbital
;
voltage clamp
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Effects of pentobarbital on the calcium current ofAplysia neurons were investigated under current- and voltage-clamp conditions using the conventional two-microelectrode technique. 2. Pentobarbital attenuated the progressive broadening of repeated action potentials of somata, suggesting a reduction in the calcium current. 3. When calcium ion was replaced with barium ion in the perfusing solution, in which neither sodium nor potassium ions carried transmembrane currents, the barium current (I Ba) which flowed through the calcium channel of the cell membrane was generated by depolarizing pulses of several hundred milliseconds applied every 1 min from a holding potential of - 50 mV. TheI Ba was not affected by tetrodotoxin (30µM). The current was decreased by pentobarbital (0.1–5 mM) in a dose-dependent manner. The inhibition was much greater at a lower pH of the perfusate, indicating that the uncharged form of the agent was responsible. 4. The voltage-dependent inactivation of theI Ba proceeded with two time constants [190 ± 21 and 2020 ± 146 msec (N = 4) at - 10 mV], both of which were shortened by adding 1 mM pentobarbital [to 120 ± 18 and 540 ± 51 msec (N = 4), respectively]. 5. TheI Ba recovered from the inactivation with two time constants [60 ± 7 and 871 ± 76 msec (N = 3) at - 50 mV]. The anesthetic (1 mM) prolonged both of them, to 124 ± 20 and 1480 ± 172 msec (N = 3), respectively, resulting in a use-dependent depression of the current at 2-Hz stimulation. 6. Pentobarbital reduced theI Ba to a greater extent when the holding potential was more positive (- 30 instead of - 50 mV), indicating a higher affinity of the drug to the inactivated state of the channel. 7. These findings suggest that the attenuation of the progressive broadening of successive spikes by pentobarbital is due to a decrease in the voltage- and time-dependent calcium current, ending in depression of transmitter release from the nerve terminal.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00711115
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