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First published online January 17, 2007
Journal of Experimental Biology 210, 454-464 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02667

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Excitable properties of adult skeletal muscle fibres from the honeybee Apis mellifera

Claude Collet^* and Luc Belzunces

Ecologie des invertébrés, INRA, Institut National de la Recherche Agronomique, UMR406, Domaine St Paul, Site Agroparc, F-84914 Avignon cedex 9, France

^* Author for correspondence (e-mail: claude.collet{at}avignon.inra.fr)

Accepted 23 November 2006

In the hive, a wide range of honeybees tasks such as cell cleaning, nursing, thermogenesis, flight, foraging and inter-individual communication (waggle dance, antennal contact and trophallaxy) depend on proper muscle activity. However, whereas extensive electrophysiological studies have been undertaken over the past ten years to characterize ionic currents underlying the physiological neuronal activity in honeybee, ionic currents underlying skeletal muscle fibre activity in this insect remain, so far, unexplored. Here, we show that, in contrast to many other insect species, action potentials in muscle fibres isolated from adult honeybee metathoracic tibia, are not graded but actual all-or-none responses. Action potentials are blocked by Cd²⁺ and La³⁺ but not by tetrodotoxin (TTX) in current-clamp mode of the patch-clamp technique, and as assessed under voltage-clamp, both Ca²⁺ and K⁺ currents are involved in shaping action potentials in single muscle fibres. The activation threshold potential for the voltage-dependent Ca²⁺ current is close to –40 mV, its mean maximal amplitude is –8.5±1.9 A/F and the mean apparent reversal potential is near +40 mV. In honeybees, GABA does not activate any ionic membrane currents in muscle fibres from the tibia, but L-glutamate, an excitatory neurotransmitter at the neuromuscular synapse induces fast activation of an inward current when the membrane potential is voltage clamped close to its resting value. Instead of undergoing desensitization as is the case in many other preparations, a component of this glutamate-activated current has a sustained component, the reversal potential of which is close to 0 mV, as demonstrated with voltage ramps. Future investigations will allow extensive pharmacological characterization of membrane ionic currents and excitation–contraction coupling in skeletal muscle from honeybee, a useful insect that became a model to study many physiological phenomena and which plays a major role in plant pollination and in stability of environmental vegetal biodiversity.

Key words: patch–clamp, skeletal muscle fibre, ion current, insect, honeybee, Apis mellifera