Ca(2+) regulation of gap junctional coupling in lens epithelial cells.
The quantitative effects of Ca(2+) signaling on gap junctional coupling in lens epithelial cells have been determined using either the spread of Mn(2+) that is imaged by its ability to quench the fluorescence of fura 2 or the spread of the fluorescent dye Alexa Fluor 594. Gap junctional coupling was unaffected by a mechanically stimulated cell-to-cell Ca(2+) wave. Furthermore, when cytosolic Ca(2+) concentration (Ca) increased after the addition of the agonist ATP, coupling was unaffected during the period that Ca was maximal. However, coupling decreased transiently approximately 5-10 min after agonist addition when Ca returned to resting levels, indicating that this transient decrease in coupling was unlikely due to a direct action of Ca on gap junctions. An increase in Ca mediated by the ionophore ionomycin that was sustained for several minutes resulted in a more rapid and sustained decrease in coupling (IC(50) ~300 nM Ca(2+), Hill coefficient of 4), indicating that an increase in Ca alone could regulate gap junctions. Thus Ca increases that occurred during agonist stimulation and cell-to-cell Ca(2+) waves were too transient to mediate a sustained uncoupling of lens epithelial cells.
Churchill
G C
GC
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Lurtz
M M
MM
Louis
C F
CF
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D005456:Fluorescent Dyes; D016257:Fura-2; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D007908:Lens, Crystalline / Q000502:physiology*; D008345:Manganese / Q000494:pharmacology; D010857:Pigment Epithelium of Eye / Q000502:physiology*; D012756:Sheep; D013997:Time Factors
D005456:Fluorescent Dyes; D008345:Manganese; D015759:Ionomycin; D000255:Adenosine Triphosphate; D002118:Calcium; D016257:Fura-2