Na+-Ca2+ exchange in human neutrophils.
The pathway for inward Ca2+ movements in isolated human neutrophils was investigated. One-way 45Ca2+ influx into resting, steady-state cells amounted to approximately 6 mumol.l cell water-1.min-1. This uptake can be entirely accounted for on the basis of a carrier-mediated exchange of external Ca2+ for internal Na+. The counter transport exhibited trans stimulation of 45Ca2+ influx by internal Na+ (Km approximately equal to 26 mM) with a Hill coefficient of approximately equal to 2.6. There was substrate saturation by external Ca2+ (Km approximately equal to 0.15 mM) and by external Na+ (Km approximately equal to 30 mM); the two ions competed for the same binding sites. The exchange was noncompetitively inhibited by benzamil (Ki approximately 75 microM) and by some other amiloride analogues bearing a substituent on the terminal nitrogen atom of the guanidino group. Membrane depolarization enhanced the rate of 45Ca2+ entry, suggesting an electrogenic process; this voltage dependence was consistent with a coupling ratio of approximately 3 Na+:1 Ca2+. Hence, the Na+-Ca2+ exchange mechanism of neutrophils displays many features in common with those of other cell types. Studies in cells exposed to the tripeptide N-formylmethionyl-leucyl-phenylalanine (FMLP) indicate activation of the counter-transport system by the chemotactic factor. Thus, Na+-Ca2+ exchange may be at least partly responsible for the increase in 45Ca2+ influx and transient rise in intracellular free Ca2+ that are seen following stimulation.
Simchowitz
L
L
Department of Medicine, John Cochran Veterans Administration Medical Center, St. Louis, Missouri.
Cragoe
E J
EJ
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D001667:Binding, Competitive; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D004563:Electrochemistry; D005110:Extracellular Space / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D002412:Cations; C013407:benzamil; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000584:Amiloride; D012964:Sodium; D002118:Calcium