ISSN:
1573-6830
Keywords:
voltage clamp in isolated dendrites
;
fast inward Na current
;
fast transient outward current
;
delayed rectification
;
voltage dependence of activation and inactivation processes
;
effects of tetrodotoxin, Cd, tetraethylammonium, and 4-aminopyridine
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Segments from the nonspiking peripheral dendrites of a crustacean coxal receptor (T fiber) were studied using the voltage clamp technique. The peripheral endings of the T fiber are sensitive to stretch applied to a specialized receptor muscle by rotation of the coxa. The intraganglionary portion of the T fiber is presynaptic to the motor neurons innervating the coxal muscle. 2. Depolarizing commands activated three separate fast channels: (i) a transient inward sodium current,INa, which is blocked by tetrodotoxin (TTX); (ii) a transient outward current,Io1, having the same voltage-dependent characteristics asINa; and (iii) a second, longer-lasting, outward current,Io2. 3. BothINa andIo1 were inactivated when segments were clamped at voltages more positive than -50 mV, whereasIo2 could be activated at voltages more positive than -50 mV. 4. Io1 andIo2 were blocked by 4-aminopyridine (4-AP) and by tetraethylammonium (TEA), althoughIo2 shows a greater sensitivity to TEA thanIo1. 5. It is suggested thatIo1 may be a factor in determining the nonspiking behavior of the dendrites and thatIo2 may limit the stretch-induced depolarization in the dendrite to a value more negative than that at which the maximum rate of transmitter release occurs. 6. In addition to the three fast currents, the presence of a slow inward and slow outward current could also be demonstrated. The effects of the slow currents were longer in segments cut from the proximal part of the dendrites.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00734716
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