Author/Editor		Križaj, David; Mercer, Aaron J; Thoreson, Wallace B; Barabas, Peter
Title		Intracellular pH modulates inner segment calcium homeostasis in vertebrate photoreceptors
Type		članek
Source		Am J Physiol, Cell Physiol
Vol. and No.		Letnik 300, št. 1
Publication year		2011
Volume		str. C187-97
Language		eng
Abstract		Neuronal metabolic and electrical activity is associated with shifts in intracellular proton activity (pH(i)) 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 (Ca(2+)) in salamander photoreceptor inner segments loaded with Ca(2+) and pH indicator dyes. Resting cytosolic pH in rods and cones in HEPES-based 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 (NH(4)Cl) depolarized photoreceptors and stimulated Ca(2+) release from internal stores yet, paradoxically, also evoked dose-dependent, reversible decreases in [Ca(2+)](i). Alkalinization-evoked [Ca(2+)](i) decreases were independent of voltage-operated and store-operated Ca(2+) entry, plasma membrane Ca(2+) extrusion and Ca(2+) sequestration into internal stores. The [Ca(2+)](i) -suppressive effects of alkalinization were antagonized by the fast Ca(2+) buffer BAPTA, suggesting that pH(i) directly regulates Ca(2+) binding to internal anionic sites. In summary, this data suggests that endogenously produced protons continually modulate the membrane potential, release from Ca(2+) stores and intracellular.
Descriptors		PHOTORECEPTORS, INVERTEBRATE HYDROGEN-ION CONCENTRATION CALCIUM SIGNAL TRANSDUCTION CYTOSOL MEMBRANE POTENTIALS URODELA