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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Calmodulin and protein kinase C regulate gap junctional coupling in lens epithelial cells

Department of Biology, Georgia State University, Atlanta, Georgia 30303

Submitted 5 August 2002 ; accepted in final form 8 August 2003

The mechanisms regulating the permeability of lens epithelial cell gap junctions in response to calcium ionophore or ATP agonist-mediated increases in cytosolic Ca²⁺ (Ca_i²⁺) have been investigated using inhibitors of calmodulin (CaM) and PKC. Cell-to-cell transfer of the fluorescent dye AlexaFluor594 decreased after the rapid and sustained increase in Ca_i²⁺ (to micromolar concentrations) observed after the addition of ionophore plus Ca²⁺ but was prevented by pretreatment with inhibitors of CaM but not PKC. In contrast, the delayed, transient decrease in cell-to-cell coupling observed after the addition of ATP that we have reported previously (Churchill G, Lurtz MM, and Louis CF. Am J Physiol Cell Physiol 281: C972-C981, 2001) could be prevented by either the direct or indirect inhibition of PKC but not by inhibition of CaM. Surprisingly, there was no change in the relative proportion of the different phosphorylated forms of lens connexin43 after this ATP-dependent transient decrease in cell-to-cell coupling. Although BAPTA-loaded cells did not display the ATP-dependent transient increase in Ca_i²⁺, the delayed, transient decrease in cell-to-cell dye transfer was still observed, indicating it was Ca_i²⁺ independent. Thus CaM-mediated inhibition of lens gap junctions is associated with sustained, micromolar Ca_i²⁺ concentrations, whereas PKC-mediated inhibition of lens gap junctions is associated with agonist activation of second messenger pathways that are independent of changes in Ca_i²⁺.

calcium; connexin43; lens gap junctions

This article has been cited by other articles:

				M. M. Lurtz and C. F. Louis Intracellular calcium regulation of connexin43 Am J Physiol Cell Physiol, December 1, 2007; 293(6): C1806 - C1813. [Abstract] [Full Text] [PDF]

				Y. Zhou, W. Yang, M. M. Lurtz, Y. Ye, Y. Huang, H.-W. Lee, Y. Chen, C. F. Louis, and J. J. Yang Identification of the Calmodulin Binding Domain of Connexin 43 J. Biol. Chem., November 30, 2007; 282(48): 35005 - 35017. [Abstract] [Full Text] [PDF]