Na/H exchange in cultured chick heart cells. pHi regulation.

Abstract

The purpose of this study was to establish the existence of Na/H exchange in cardiac muscle and to evaluate the contribution of Na/H exchange to pHi regulation . The kinetics of pH i changes in cultured chick heart cells were monitored microfluorometrically with 6-carboxyfluorescein and correlated with Nai content changes analyzed by atomic absorption spectrophotometry ; transmembrane H+ movements were evaluated under pH stat conditions . After induction of an intracellular acid load by pretreatment with NH 4C1, a regulatory cytoplasmic alkalinization occurred with a t1/2 of 2.9 min. pHi regulation required external Na' and was concomitant with transmembrane H+ extrusion as well as a rapid rise in Nai content in an Na/H ratio of 1 :1 . Microelectrode recordings of membrane potential demonstrated directly the electroneutral character of pHi regulation . Acid-induced net Na' uptake could be either stimulated by further decreasing pHi or inhibited by decreasing pH .; Na' uptake was unaffected by tetrodotoxin (10 ug/ml), quinidine (10-3 M), DIDS (10-4 M), C16-free solution, or HC03-free solution . Amiloride (10-3 M) maximally inhibited both pHi regulation and Na' uptake ; the ID 3a for amiloride inhibition of Na* uptake was 3 I.M . Na.-dependent H+ extrusion showed halfmaximal activation at 15 mM Na.; Li+, but not K+ or choline', could substitute for Na' to support H+ extrusion. Ca.-free solution also stimulated acid-induced Na* uptake . We conclude that pHi regulation following an acid load in cardiac muscle cells is by an amiloride-sensitive, electroneutral Na/H exchange. Stimulation of Na/H exchange up to 54 pmol/cm2 .s indicates the rapidity of this exchange across cardiac cell membranes. Na/H exchange may also participate in steady state maintenance of pHi.

The regulation of cytosolic pH in isolated presynaptic nerve terminals from rat brain.

“…The Na+/H + antiporter was found to be the primary mechanism for regulating pHi in rat brain synaptosomes and is remarkably similar to the antiporter found in a variety of mammalian cells, e.g., fibroblasts (Moolenaar et al, 1984), lymphocytes (Grinstein et al, 1984), heart cells (Piwnica-Worms et al, 1985), and collecting tubules (Chaillet et al, 1985). Thus, it is activated by Na § and by acidification of the cytosol, and is blocked by micromolar concentrations of amiloride.…”

Effects of sodium‐potassium pump inhibition and low sodium on membrane potential in cultured embryonic chick heart cells.

“…hyperpolarization was 49-3 + 1-2 mV (n = 3) and this was not significantly affected (F test, P > 0 25) by 16 jtM-tetrodotoxin (TTX) or 1 mM-amiloride in the presence of which the hyperpolarizations were 43 0 + 4-0 mV (n = 3) and 45-7 + 07 mV (n = 3) respectively: amiloride almost completely blocks Na+-H+ exchange in this preparation at 0-1 mM (Piwnica-Worms, Jacob, Horres & Lieberman, 1985 Another possibility is that lowering the Na+ reversal potential, ENa, by partial removal of external Na+ will cause ENa to shift in a negative direction and could cause a shift in Em towards EK if there was any significant permeability to Na+. To reduce the possibility of these effects, we repeated the experiment in a [K+].…”

Reactive oxygen species-mediated regulation of the Na+–H+ exchanger 1 gene expression connects intracellular redox status with cells' sensitivity to death triggers

“…In contrast, in cells with a higher steadystate production of acid, varying NHE1 activity or expression may alter intracellular pH more markedly. For example, heart cells have a high rate of metabolism, 33 and it has been demonstrated that the Na þ /H þ exchanger has a role in steady-state pH regulation. Small though detectable, steadystate rates of Na þ /H þ exchange also occur in neuroblastoma cells 34 and necturus gallbladder, 35 but steady-state pH regulation by the Na þ /H þ exchanger is not detectable in cultured skeletal muscle cells 36 and thymic lymphocytes.…”