Calcium regulation by lens plasma membrane vesicles

Arch Biochem Biophys. 1988 Aug 1;264(2):472-81. doi: 10.1016/0003-9861(88)90312-8.


The role of the plasma membrane in the regulation of lens fiber cell cytosolic Ca2+ concentration has been examined using a vesicular preparation derived from calf lenses. Calcium accumulation by these vesicles was ATP dependent, and was releasable by the ionophore A23187, indicating that calcium was transported into a vesicular space. Calcium accumulation was stimulated by Ca2+ (K1/2 = 0.08 microM Ca2+) potassium (maximally at 50 mM K+), and cAMP-dependent protein kinase; it was inhibited by both vanadate (IC50 = 5 microM) and the calmodulin inhibitor R24571 (IC50 = 5 microM), indicating that this pump was plasma-membrane derived and likely calmodulin dependent. Valinomycin, in the presence of K+, stimulated calcium uptake, suggesting that the calcium pump either countertransports K+, or is regulated in an electrogenic fashion. Inhibition of calcium uptake by selenite and p-chloromercuribenzoate demonstrates the presence of an essential -SH group(s) in this enzyme. Calcium release from calcium-filled lens vesicles was enhanced by Na+, demonstrating that these vesicles also contain a Na:Ca exchange carrier. p-Chloromercuribenzoate and p-chloromercuribenzoate sulfonic acid also promoted calcium release from calcium-filled vesicles, suggesting that this release, like calcium uptake, is in part mediated by a cysteine-containing protein. We conclude that lens fiber cell cytosolic Ca2+ concentration could be regulated by a number of plasma membrane processes. The sensitivity of both calcium uptake and release to -SH reagents has implications in lens cataract formation, where oxidation of lens proteins has been proposed to account for the elevated cytosolic Ca2+ in this condition.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4-Chloromercuribenzenesulfonate / pharmacology
  • Adenosine Triphosphate / pharmacology
  • Animals
  • Calcimycin / pharmacology
  • Calcium / metabolism*
  • Calmodulin / antagonists & inhibitors
  • Calmodulin / pharmacology
  • Carrier Proteins / metabolism
  • Cattle
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism*
  • Chloromercuribenzoates / pharmacology
  • Cyclic AMP / pharmacology
  • Cytosol / metabolism
  • Imidazoles / pharmacology
  • Lens, Crystalline / metabolism*
  • Membrane Proteins / metabolism
  • Potassium / pharmacology
  • Protein Kinases / pharmacology
  • Sodium-Calcium Exchanger
  • Sodium-Potassium-Exchanging ATPase / metabolism
  • Valinomycin / pharmacology
  • Vanadates / pharmacology
  • p-Chloromercuribenzoic Acid


  • Calmodulin
  • Carrier Proteins
  • Chloromercuribenzoates
  • Imidazoles
  • Membrane Proteins
  • Sodium-Calcium Exchanger
  • Valinomycin
  • Calcimycin
  • Vanadates
  • calmidazolium
  • p-Chloromercuribenzoic Acid
  • 4-Chloromercuribenzenesulfonate
  • Adenosine Triphosphate
  • Cyclic AMP
  • Protein Kinases
  • Sodium-Potassium-Exchanging ATPase
  • Potassium
  • Calcium