A persistent sodium current contributes to oscillatory activity in heart interneurons of the medicinal leech

✍ Scribed by C. A. Opdyke; R. L. Calabrese

• Publisher: Springer
• Year: 1994
• Tongue: English
• Weight: 992 KB
• Volume: 175
• Category: Article
• ISSN: 0340-7594
• DOI: 10.1007/bf00191850

✦ Synopsis

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. 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. 3. Plateaus in heart interneurons induced by Co ++ and internal TEA + involve a conductance increase. 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 +. 5. Calcium channel blockers such as La 3+ and Co ++ block neither the TEA + induced plateaus nor I e, suggesting that Na + is not using Ca ++ channels. Moreover, I e is enhanced by Ca++-free Co++-containing salines. Thus, Ip is correlated with the TEA +-and Co++-induced plateau behavior.