Cell alkalosis elevates cytosolic Ca2+ in rabbit resident alveolar macrophages.
Disruption of cellular acid-base status alters the host defence functions of alveolar macrophages (m phi). These pH effects might be mediated by pH-sensitive changes in the signalling pathways of the effector functions of m phi. The present study examined the effects of intracellular pH (pH(i)) on the free cytosolic calcium concentration ([Ca(2+)](i)), an important second messenger for cell functions. [Ca(2+)](i) and pH(i) of rabbit resident alveolar m phi were measured using fluorescent dyes. With extracellular pH (pH(o)) of 7.4, the steady-state pH(i) and [Ca(2+)](i) were approx. 7.14 and 123 nM respectively. Incubation at pH(o) 6.8 caused a sustained cytosolic acidosis, but did not affect [Ca(2+)](i). Likewise, [Ca(2+)](i) was unchanged when m phi at pH(o) 7.4 were acidified using bafilomycin A(1) or sodium propionate. In contrast, [Ca(2+)](i) was markedly sensitive to cytosolic alkalosis. Exposure to NH(4)Cl at pH(o) 7.4 caused transient increases in both pH(i) and [Ca(2+)](i). The Ca(2+) response was mediated by release of intracellular Ca(2+) from thapsigargin-sensitive stores and was potentiated by capacitative entry of extracellular Ca(2+). Incubation at high pH(o) values (>7.4) produced sustained increases in pH(i) and [Ca(2+)](i). The sustained elevation of [Ca(2+)](i) was consistent with pH-sensitive inhibition of plasma-membrane Ca(2+)-ATPase. The response to high pH(o) was unaffected by blockade of L-type or receptor-operated Ca(2+) channels with nifedipine or SKF-96365, and was independent of extracellular Na(+). The findings indicate that pH impacts cytosolic Ca(2+) homoeostasis at multiple levels. The data suggest that cellular acid-base status can influence Ca(2+)-dependent signalling events in resident alveolar m phi, especially during alkaline disruptions of pH(i).
Heming
Thomas A
TA
Department of Internal Medicine, University of Texas Health Science Center, Houston, TX 77030, USA. thomas.heming@uth.tmc.edu
Bulayeva
Nataliya N
NN
Bidani
Akhil
A
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D006863:Hydrogen-Ion Concentration; D018942:Macrolides; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D011422:Propionates / Q000494:pharmacology; D011817:Rabbits; D015290:Second Messenger Systems / Q000502:physiology*; D013050:Spectrometry, Fluorescence; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors
D000900:Anti-Bacterial Agents; D005456:Fluorescent Dyes; D018942:Macrolides; D011422:Propionates; D000643:Ammonium Chloride; C040929:bafilomycin A1; C514135:sodium propionate; D025262:Vacuolar Proton-Translocating ATPases; C029658:propionic acid; D002118:Calcium; D016257:Fura-2