Summary
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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.
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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.
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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.
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4.
Io1 andIo2 were blocked by 4-aminopyridine (4-AP) and by tetraethylammonium (TEA), althoughIo2 shows a greater sensitivity to TEA thanIo1.
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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.
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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.
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Mirolli, M. Inward and outward currents in isolated dendrites of crustacea coxal receptors. Cell Mol Neurobiol 3, 355–370 (1983). https://doi.org/10.1007/BF00734716
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DOI: https://doi.org/10.1007/BF00734716