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First published online June 29, 2007
Journal of Experimental Biology 210, 2489-2500 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006361

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Properties and possible function of a hyperpolarisation-activated chloride current in Drosophila

Uwe Rose^1,*, Christian Derst², Mario Wanischeck¹, Christiane Marinc¹ and Christian Walther³

¹ Institute of Neurobiology, University Ulm, Albert-Einstein-Allee 11, Ulm 89160, Germany
² Institute for Integrative Neuroanatomy, Charite, Berlin, Germany
³ Institute of Physiology and Pathophysiology, Philipps University Marburg, Marburg, Germany

^* Author for correspondence (e-mail: uwe.rose{at}uni-ulm.de)

Accepted 2 May 2007

A chloride current, I_Cl,H, slowly activating on hyperpolarisation was investigated in Drosophila melanogaster larval muscles using the two-electrode voltage clamp. Sizeable currents were observed after the intracellular chloride concentration ([Cl^–]_i) had been elevated by diffusion of Cl^– from the electrodes. The time course of I_Cl,H was rather variable and required two exponentials to be accurately described. The reversal potential, –40 to –20 mV in Cl^–-loaded fires, shifted on lowering external [Cl^–] in the positive direction. Steady-state activation of I_Cl,H was characterised by V_0.5 of –120 mV and a slope factor, k, of 10 mV at a [Cl^–]_i 35 mmol l^–1. Raising [Cl^–]_i to 50 mmol l^–1 caused a negative shift of V_0.5 equivalent to the change of E_Cl and led to a nearly threefold increase in maximal steady-state conductance. I_Cl,H was resistant to 10 mmol l^–1 Zn²⁺ and 1 mmol l^–1 Cd²⁺ but was greatly reduced by 1 mmol l^–1 9-anthracenecarboxylic acid (9-AC). I_Cl,H was affected by changes of extracellular pH and increased on lowering extracellular osmolality. 9-AC also decreased muscle fibre resting conductance by approximately 20% and increased muscle contractions. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis confirmed the expression of all three ClC genes in muscle, and immunohistochemistry indicated location of Drosophila melanogaster chloride channel-2 (DmClC-2) at the Z-lines. We conclude that DmClC-2 accounts for the channels underlying I_Cl,H, and in part for the resting chloride conductance. DmClC-2 may serve general homeostatic mechanisms such as pH- and osmo-regulation or may support muscle function on high motor activity or during a particular neurohormonal state of the animal.

Key words: ClC-2, chloride current, homeostasis, cellular excitation, Drosophila

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