Na⁺/H⁺ exchange and pH regulation in the control of neutrophil chemokinesis and chemotaxis

Abstract

Large proton fluxes accompany cell migration, but their precise role remains unclear. We studied pH regulation during the course of chemokinesis and chemotaxis in human neutrophils stimulated by attractant peptides. Activation of cell motility by chemoattractants was accompanied by a marked increase in metabolic acid generation, attributable to energy consumption by the contractile machinery and to stimulation of the NADPH oxidase and the ancillary hexose monophosphate shunt. Despite the increase in acid production, the cytosol underwent a sizable alkalinization, caused by acceleration of Na ϩ /H ϩ exchange. The development of the alkalinization mirrored the increase in the rate of cell migration, suggesting a causal relationship. However, elimination of Na ϩ /H ϩ exchange by omission of external Na ϩ or by addition of potent inhibitors was without effect on either chemokinesis or chemotaxis, provided the cytosolic pH remained near neutrality. At more acidic levels, cell motility was progressively inhibited. These observations suggest that Na ϩ /H ϩ exchange plays a permissive role in cell motility but is not required for the initiation or development of the migratory response. Chemokinesis also was found to be exquisitely sensitive to extracellular acidification. This property may account for the inability of neutrophils to access abscesses and solid tumors that have been reported to have inordinately low pH.

Voltage-gated proton channels maintain pH in human neutrophils during phagocytosis

“…In cells exhibiting recovery, the nadir occurred after 3.4 Ϯ 2.0 min (SD, n ϭ 58). The large decrease in pH i in phagocytosing neutrophils was unexpected and greatly exceeds reported responses (1,(3)(4)(5)7). This apparent discrepancy is likely attributable mainly to the smearing of time courses of individual cells by averaging, inclusion of nonresponding cells, and use of soluble stimuli in previous studies.…”

“…For 3 decades, pH i during the respiratory burst has been characterized as a small (0.05-0.1 unit) transient drop in pH i that is followed by larger (0.16-0.60 unit) prolonged alkalinization caused by Na ϩ /H ϩ antiport activity, whether the stimulus is fMLF (fMetLeuPhe, a chemotactic peptide), PMA (a PKC-activating phorbol ester), phospholipase C, or OPZ (opsonized zymosan) (1)(2)(3)(4)(5)(6)(7). In most studies, soluble stimuli were applied to populations of neutrophils.…”

Regulation of Early Neurite Morphogenesis by the Na+/H+ Exchanger NHE1

“…Similarly, although NHE1 is required for maximally efficient cell migration in non-neuronal cells, it is not essential for the development of the migratory response (Hayashi et al, 2008). The fact that NHE1-null mice, although exhibiting a distinctive neurological phenotype that includes ataxia, truncal instability, seizures, and selective neuronal death, do not display gross neurodevelopmental defects (Cox et al, 1997;Bell et al, 1999) also points to a permissive role for NHE1 in neurite morphogenesis, although it must be noted that interpretation of the NHE1 Ϫ/Ϫ phenotype is complicated by alterations in the expression and/or activities of other pH i regulating mechanisms and Na ϩ influx pathways in NHE1 Ϫ/Ϫ neurons that compensate for the loss of NHE1 (Xia et al, 2003;Xue et al, 2003;Schwab et al, 2005) (see also Putney and Barber, 2004;Zhou et al, 2004).…”

“…In migrating cells, for example, NHE1 accumulates at the leading edge to regulate the dynamic reorganization of the actin cytoskeleton and polarized membrane protrusion, and reductions in ion translocation activity or mutations that disrupt actin cytoskeletal anchoring and thereby mislocalize NHE1 away from the leading edge impair directional motility (Grinstein et al, 1993;Denker et al, 2000;Klein et al, 2000;Lagana et al, 2000;Denker and Barber, 2002;Stüwe et al, 2007;Hayashi et al, 2008;Schneider et al, 2009).…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…fibroblasts, MDCK cells), however there is data to suggest this is not a universal phenomenon. Inhibition of NHE1 transport in granulocytes does not affect chemotaxis and chemokinesis [63]. Furthermore, NHE1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 knock-out (KO) mice exhibit normal embryogenesis, suggesting redundant or compensatory mechanisms [34,15].…”