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Journal of Experimental Biology 133,231-248 (1987)
Published by Company of Biologists 1987

Properties and Pharmacology of a TTX-insensitive Na⁺ Current in Neurones of the Jellyfish Cyanea Capillata

PETER A. V. ANDERSON ¹

¹ Whitney Laboratory and Departments of Physiology and Neuroscience, University of Florida, St Augustine, Fl 32086, USA

Neurones of the motor nerve net of the jellyfish Cyanea capillata were axotomized, and voltage-clamped using the whole-cell configuration of the patch-clamp technique.

Outward currents were blocked by a combination of extracellular 4-aminopyridine (4-AP) and intracellular Cs⁺, tetraethylammonium (TEA⁺) and 4-AP.

Under normal conditions, the inward current consisted of a fast, transient current which could be abolished by removal of extracellular Na⁺ and whose reversal potential was dependent on the extracellular Na⁺ concentration.

This current was completely insensitive to tetrodotoxin (TTX), saxitoxin (STX) and conotoxin GIIIA but could be blocked by extracellular Cd²⁺, lidocaine, W7 [N-(6 aminohexyl)-5-chloro-1-napthalenesulphonamide] and verapamil.

Inactivation was voltage-dependent with a V_h of -15mV, and was unaffected by veratridine, batrachotoxin (BTX), sea anemone toxin and scorpion (Leiurus) venom. Reactivation required repolarization to a negative membrane potential for 12 ms for half-maximal reactivation.

In the absence of extracellular Na⁺ no inward current was visible unless [Ca²⁺]_o was elevated. In Na⁺-free, 95 mmoll^-1 Ca²⁺ saline, a slightly slower, inward current was recorded. This current is believed to be the Ca²⁺ current that underlies synaptic transmission.

7. These findings are discussed with reference to synaptic transmission in these cells and the evolution of ion channels.

Key words: sodium current, calcium current, jellyfish, coelenterate, voltage-clamp, scyphozoa

Accepted on July 9, 1987

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