Purinergic activation of anion conductance and osmolyte efflux in cultured rat hippocampal neurons

Abstract

Li G, Olson JE. Purinergic activation of anion conductance and osmolyte efflux in cultured rat hippocampal neurons. Am J Physiol Cell Physiol 295: C1550 -C1560, 2008. First published October 15, 2008 doi:10.1152/ajpcell.90605.2007.-The majority of mammalian cells demonstrate regulatory volume decrease (RVD) following swelling caused by hyposmotic exposure. A critical signal initiating RVD is activation of nucleotide receptors by ATP. Elevated extracellular ATP in response to cytotoxic cell swelling during pathological conditions also may initiate loss of taurine and other intracellular osmolytes via anion channels. This study characterizes neuronal ATPactivated anion current and explores its role in net loss of amino acid osmolytes. To isolate anion currents, we used CsCl as the major electrolyte in patch electrode and bath solutions and blocked residual cation currents with NiCl 2 and tetraethylammonium. Anion currents were activated by extracellular ATP with a K m of 70 M and increased over fourfold during several minutes of ATP exposure, reaching a maximum after 9.0 min (SD 4.2). The currents were blocked by inhibitors of nucleotide receptors and volume-regulated anion channels (VRAC). Currents showed outward rectification and inactivation at highly depolarizing membrane potentials, characteristics of swelling-activated anion currents. P2X agonists failed to activate the anion current, and an inhibitor of P2X receptors did not block the effect of ATP. Furthermore, current activation was observed with extracellular ADP and 2-(methylthio)adenosine 5Ј-diphosphate, a P2Y 1 receptor-specific agonist. Much less current activation was observed with extracellular UTP, suggesting the response is mediated predominantly by P2Y 1 receptors. ATP caused a dose-dependent loss of taurine and alanine that could be blocked by inhibitors of VRAC. ATP did not inhibit the taurine uptake transporter. Thus extracellular ATP triggers a loss of intracellular organic osmolytes via activation of anion channels. This mechanism may facilitate neuronal volume homeostasis during cytotoxic edema. amino acids; taurine; cell volume EXTRACELLULAR PURINE AND PYRIMIDINE compounds mediate a variety of brain functions by receptor-mediated action. Extracellular ATP and its metabolic products can initiate cellular responses through two types of receptors: P1 receptors, which are highly sensitive to adenosine, and P2 receptors, sensitive to adenine nucleotides. The P2 receptors are further divided into P2X (ligand-gated channels) or P2Y (G protein-coupled receptors) (1,65,66,77). These receptors are widely distributed in the central nervous system and provoke a variety of effects on neurons and on glial cells.

Adhesion to Carbon Nanotube Conductive Scaffolds Forces Action-Potential Appearance in Immature Rat Spinal Neurons

“…We believe that this is a genuine phenomenon, in fact previous reports in analogous recording conditions ruled out the possibility that similar or even higher capacitance values in control neurons might limit space-clamp significantly, impairing the detection of action potential or voltage activated currents [22,53–55]. MWCNT growth supports were reported to affect various aspects of excitable cell function in culture [22–24,26,28].…”

Neurites outgrowth and amino acids levels in goldfish retina under hypo‐osmotic or hyper‐osmotic conditions

“…The efflux of taurine, taking place during the hypo‐osmotic shock, might be responsible for the reduction of the outgrowth. Most cells swell following hypo‐osmotic exposure, which could be cytotoxic and produce loss of taurine from the intracellular space, a process associated to elevated extracellular ATP (Li and Olson, 2008).…”

Extracellular osmolarity modulates G protein-coupled receptor-dependent ATP release from 1321N1 astrocytoma cells

“…For example, autocrine activation of P2 receptors in astrocytes, hepatocytes, or airway epithelial cells by endogenous ATP released in response to hypotonic stress accelerates the efflux of Cl Ϫ and organic osmolytes that facilitate RVD responses. Scavenging of extracellular ATP by added nucleotidases or blockade of P2 receptors during exposure to hypotonic stress can interrupt these purinergic autocrine loops and attenuate or slow cell volume recovery from swelling (13,16,21,34,35,43,48,70,74). Protease-activated receptors and other sensors of local tissue damage/stress can modulate brain injury.…”

“…1321N1 cells present an additional advantage for analysis of the signaling mechanisms that couple GPCR to VRAC/VSOAC activation (or other GPCR-regulated permeability pathways) because they lack endogenous expression of G protein-coupled P2Y receptors. This is germane because P2Y receptors also activate VRAC/VSOAC in primary astrocytes and other cell types (35,44,45,57). Thus, ATP released in response to hypotonic stress or other GPCR agonists can act as an autocrine modulator or amplifier of VRAC/VSOAC and volume regulatory responses.…”