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Journal of Experimental Biology 155,435-453 (1991)
Published by Company of Biologists 1991

Sodium- and Calcium-Dependent Excitability of Embryonic Leech Ganglion Cells in Culture

KARIN SCHIRRMACHER ¹ and JOACHIM W. DEITMER ²

¹ Institut für Zoologie/Neurobiologie, Heinrich-Heine Universität, D-4000 Düsseldorf, FRG
² Abteilung für Allgemeine Zoologie, FB Biologie, Universität Kaiserlautern, Postfach 3049, D-6750 Kaiserslautern, FRG

To whom reprint requests should be addressed

Voltage-dependent Na⁺ and Ca²⁺ inward currents underlying the action potential in cultured embryonic ganglion cells of the leech Hirudo medicinalis have been investigated using the gigaseal whole-cell current or voltage-clamp technique. Dissociated ganglion cells were isolated from 7- to 14-day-old embryos, and maintained in primary culture for up to 5 days. More than 95% of the cultured cells had voltage-dependent K⁺ currents and about 75% of the cells had voltagedependent inward currents. Action potentials of 60mV amplitude and 4 ms duration, similar to those in embryonic nerve cells in vivo, could be recorded. Three types of inward currents occurred in these cells: (1) an initial Na⁺ current, which activated and inactivated rapidly; (2) a second Na⁺ current, which activated slowly and persisted during membrane depolarization, showing very little inactivation, and (3) a Ca²⁺-dependent inward current. Both types of Na⁺ currents were resistant to tetrodotoxin (TTX, 0.2–5 µmol l^-1). The Ca⁺ current was also carried by Ba²⁺, and was blocked by cobalt and cadmium. The fast Na⁺ current was first expressed in cells from 8-day-old embryos, 1 day earlier than the Ca²⁺ current. Between days 8 and 14 the density of the fast Na⁺ current increased from 22±3 to 51±6 µA cm^-2 (±S.D., N=11), while the Ca²⁺ current grew from 10 µA cm^-1 (N=2) to 15±4 µA cm^-2 (N=10) during this time.

Key words: Na⁺-dependent excitability, Ca²⁺-dependent excitability, leech ganglion cells, whole-cell current recordings, Hirudo medicinalis

Accepted on July 12, 1990

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