A persistent sodium current contributes to oscillatory activity in heart interneurons of the medicinal leech.
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 voltage-clamp 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 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.
Opdyke
C A
CA
Department of Biology, Emory University, Atlanta, GA 30322.
Calabrese
R L
RL
D000818:Animals; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D006329:Heart Conduction System / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D007865:Leeches / Q000502:physiology*; D009991:Oscillometry; D010507:Periodicity; D012964:Sodium / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D002121:Calcium Channel Blockers; D013757:Tetraethylammonium Compounds; D003035:Cobalt; D019789:Tetraethylammonium; D012964:Sodium; D002118:Calcium