Intracellular pH modulates inner segment calcium homeostasis in vertebrate photoreceptors

David Križaj, Aaron J. Mercer, Wallace B. Thoreson, Peter Barabas

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Neuronal metabolic and electrical activity is associated with shifts in intracellular pH (pHi) proton activity and state-dependent changes in activation of signaling pathways in the plasma membrane, cytosol, and intracellular compartments. We investigated interactions between two intracellular messenger ions, protons and calcium (Ca2+), in salamander photoreceptor inner segments loaded with Ca2+ and pH indicator dyes. Resting cytosolic pH in rods and cones in HEPESbased saline was acidified by ∼0.4 pH units with respect to pH of the superfusing saline (pH = 7.6), indicating that dissociated inner segments experience continuous acid loading. Cytosolic alkalinization with ammonium chloride (NH4Cl) depolarized photoreceptors and stimulated Ca2+ release from internal stores, yet paradoxically also evoked dose-dependent, reversible decreases in [Ca 2+]i. Alkalinization-evoked [Ca2+]i decreases were independent of voltage-operated and store-operated Ca2+ entry, plasma membrane Ca2+ extrusion, and Ca2+ sequestration into internal stores. The [Ca2+]i-suppressive effects of alkalinization were antagonized by the fast Ca2+ buffer BAPTA, suggesting that pHi directly regulates Ca2+ binding to internal anionic sites. In summary, this data suggest that endogenously produced protons continually modulate the membrane potential, release from Ca2+ stores, and intracellular Ca2+ buffering in rod and cone inner segments.

Original languageEnglish (US)
Pages (from-to)C187-C197
JournalAmerican Journal of Physiology - Cell Physiology
Volume300
Issue number1
DOIs
StatePublished - Jan 2011

Keywords

  • Alkalinization
  • Proton
  • Ryanodine store
  • Store operated
  • Voltage operated

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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