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This Article Full Text Full Text (PDF) All Versions of this Article: 295/5/C1454    most recent 00535.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kaba, N. K. Articles by Knauf, P. A. Search for Related Content PubMed PubMed Citation Articles by Kaba, N. K. Articles by Knauf, P. A.

VASCULAR BIOLOGY

Inhibition of Na⁺/H⁺ exchanger enhances low pH-induced L-selectin shedding and β₂-integrin surface expression in human neutrophils

Nubia K. Kaba, Joanne Schultz, Foon-Yee Law, Craig T. Lefort, Guadalupe Martel-Gallegos, Minsoo Kim, Richard E. Waugh, Jorge Arreola, and Philip A. Knauf

Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York

Submitted 10 November 2007 ; accepted in final form 22 September 2008

Ischemia-reperfusion injury is a common pathological occurrence causing tissue damage in heart attack and stroke. Entrapment of neutrophils in the vasculature during ischemic events has been implicated in this process. In this study, we examine the effects that lactacidosis and consequent reductions in intracellular pH (pH_i) have on surface expression of adhesion molecules on neutrophils. When human neutrophils were exposed to pH 6 lactate, there was a marked decrease in surface L-selectin (CD62L) levels, and the decrease was significantly enhanced by inclusion of Na⁺/H⁺ exchanger (NHE) inhibitor 5-(N,N-hexamethylene)amiloride (HMA). Similar effects were observed when pH_i was reduced while maintaining normal extracellular pH, by using an NH₄Cl prepulse followed by washes and incubation in pH 7.4 buffer containing NHE inhibitors [HMA, cariporide, or 5-(N,N-dimethyl)amiloride (DMA)]. The amount of L-selectin shedding induced by different concentrations of NH₄Cl in the prepulse correlated with the level of intracellular acidification with an apparent pK of 6.3. In contrast, β₂-integrin (CD11b and CD18) was only slightly upregulated in the low-pH_i condition and was enhanced by NHE inhibition to a much lesser extent. L-selectin shedding was prevented by treating human neutrophils with inhibitors of extracellular metalloproteases (RO-31-9790 and KD-IX-73-4) or with inhibitors of intracellular signaling via p38 MAP kinase (SB-203580 and SB-239063), implying a transmembrane effect of pH_i. Taken together, these data suggest that the ability of NHE inhibitors such as HMA to reduce ischemia-reperfusion injury may be related to the nearly complete removal of L-selectin from the neutrophil surface.

integrins; p38 mitogen-activated protein kinase; ischemia-reperfusion; Na⁺/H⁺ exchanger inhibitors; lactate