Abstract
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1.
Normal activity in bilateral pairs of heart interneurons, from ganglia 3 or 4, in the medicinal leech (Hirudo medicinalis) is antiphasic due to their reciprocally inhibitory connections. However, Ca+-free Co+-containing salines lead to synchronous oscillations in these neurons.
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2.
Internal TEA+ allows expression of full plateaus during Co++ induced oscillations in heart interneurons; these plateaus are not blocked by Cs+. Similar plateaus are also observed with internal TEA+ alone, but under these conditions activity in heart interneurons from ganglia 3 or 4 is antiphasic.
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3.
Plateaus in heart interneurons induced by Co++ and internal TEA+ involve a conductance increase.
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4.
A voltage-dependent inward current, IP, showing little inactivation, was isolated using single-electrode voltageclamp in heart interneurons. This current is carried at least in part by Na+; the current is reduced when external Na+ is reduced and is carried by Li+ when substituted for Na+.
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5.
Calcium channel blockers such as La3+ and Co++ block neither the TEA+ induced plateaus nor IP, suggesting that Na+ is not using Ca++ channels. Moreover, IP is enhanced by Ca++-free Co++-containing salines. Thus, IP is correlated with the TEA+- and Co++-induced plateau behavior.
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Abbreviations
- HEPES :
-
N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid
- TEA :
-
tetraethylammonium
- V h :
-
holding potential
- HN :
-
heart interneuron
- SEVC :
-
single-electrode-voltage-clamp
- STX :
-
Saxitoxin
- TTX :
-
Tetrodotoxin
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Opdyke, C.A., Calabrese, R.L. A persistent sodium current contributes to oscillatory activity in heart interneurons of the medicinal leech. J Comp Physiol A 175, 781–789 (1994). https://doi.org/10.1007/BF00191850
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DOI: https://doi.org/10.1007/BF00191850