Stimulation of L-type Ca(2+) channels by increase of intracellular InsP3 in rat retinal pigment epithelial cells

Exp Eye Res. 2002 Jan;74(1):29-40. doi: 10.1006/exer.2001.1128.


The purpose of this study was to investigate the role of voltage-dependent L-type Ca(2+)channels in intracellular Ca(2+)signaling of the retinal pigment epithelium (RPE). Patch-clamp techniques in conjunction with measurements of the intracellular free Ca(2+)using the Ca(2+)-sensitive fluorescence dye fura-2 were performed using cultured rat RPE cells. Intracellular application of inositol-1,4,5-trisphosphate (InsP3; 10 microM) via the patch-pipette during the whole-cell configuration led to an increase in the intracellular free Ca(2+)([Ca(2+)](i)). This effect could be reduced by the L-type Ca(2+)channel blocker nifedipine (2 microM). At the moment of the maximal rise in [Ca(2+)](i)L-type currents displayed an increase in the current density and shifts in the activation curve and of the steady-state inactivation. Comparable changes of L-type channel activity could be observed by induction of capacitative Ca(2+)entry, a maneuver to release Ca(2+)from intracellular Ca(2+)stores independently from InsP3. The increase in L-type Ca(2+)channel activity and [Ca(2+)](i)by intracellular application of InsP3 or induction of capacitative Ca(2+)entry could be inhibited by blocking tyrosine kinase activity using genistein (5 microM) or tyrphostin 51 (10 microM). It is concluded that L-type Ca(2+)channels are involved in the Ca(2+)/InsP3 second messenger system by generating an influx of extracellular Ca(2+)into the cell. This is enabled by depletion of cytosolic Ca(2+)stores and tyrosine kinase-dependent activation of L-type channels.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium Channels, L-Type / drug effects
  • Calcium Channels, L-Type / physiology*
  • Cells, Cultured
  • Cytosol / metabolism
  • Enzyme Inhibitors / pharmacology
  • Genistein / pharmacology
  • Inositol 1,4,5-Trisphosphate / pharmacology*
  • Patch-Clamp Techniques
  • Pigment Epithelium of Eye / cytology
  • Pigment Epithelium of Eye / drug effects
  • Pigment Epithelium of Eye / metabolism*
  • Protein-Tyrosine Kinases / antagonists & inhibitors
  • Protein-Tyrosine Kinases / physiology
  • Rats
  • Second Messenger Systems / physiology
  • Tyrphostins / pharmacology


  • Calcium Channels, L-Type
  • Enzyme Inhibitors
  • Tyrphostins
  • tyrphostin 51
  • Inositol 1,4,5-Trisphosphate
  • Genistein
  • Protein-Tyrosine Kinases
  • Calcium