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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Intracellular calcium regulation of connexin43

Department of Cell Biology and Neuroscience, University of California, Riverside, California

Submitted 22 December 2006 ; accepted in final form 24 September 2007

The mechanism by which intracellular Ca²⁺ concentration ([Ca²⁺]_i) regulates the permeability of gap junctions composed of connexin43 (Cx43) was investigated in HeLa cells stably transfected with this connexin. Extracellular addition of Ca²⁺ in the presence of the Ca²⁺ ionophore ionomycin produced a sustained elevation in [Ca²⁺]_i that resulted in an inhibition of the cell-to-cell transfer of the fluorescent dye Alexa fluor 594 (IC₅₀ of 360 nM Ca²⁺). The Ca²⁺ dependency of this inhibition of Cx43 gap junctional permeability is very similar to that described in sheep lens epithelial cell cultures that express the three sheep lens connexins (Cx43, Cx44, and Cx49). The intracellular Ca²⁺-mediated decrease in cell-to-cell dye transfer was prevented by an inhibitor of calmodulin action but not by inhibitors of Ca²⁺/calmodulin-dependent protein kinase II or protein kinase C. In experiments that used HeLa cells transfected with a Cx43 COOH-terminus truncation mutant (Cx43²⁵⁷), cell-to-cell coupling was similarly decreased by an elevation of [Ca²⁺]_i (IC₅₀ of 310 nM Ca²⁺) and similarly prevented by the addition of an inhibitor of calmodulin. These data indicate that physiological concentrations of [Ca²⁺]_i regulate the permeability of Cx43 in a calmodulin-dependent manner that does not require the major portion of the COOH terminus of Cx43.

gap junction; calmodulin; HeLa cells; lens epithelium

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