Effects of particulate and soluble (1-3)-beta-glucans on Ca2+ influx in NR8383 alveolar macrophages.
Particulate and soluble (1-3)-beta-glucans are effective in preventing infections by enhancing macrophage and neutrophil functions. However, the mechanisms triggering these enhanced cellular responses are essentially unknown. We recently demonstrated that zymosan, a particulate (1-3)-beta-glucan receptor agonist, caused an influx of Ca2+ in NR8383 rat alveolar macrophages (AMs) and a resulting increase in intracellular Ca2+ (Zhang et al., J. Leukoc. Biol. 62 (1997) 341-348). Since Ca2+ is important in mediating leukocyte responses, we investigated whether other (1-3)-beta-glucans also alter Ca2+ mobilization in AMs. Particulate and soluble (1-3)-beta-glucans derived from Saccharomyces cerevisiae were used in these studies. Like zymosan, particulate (1-3)-beta-glucan (WGPs) caused a concentration-dependent increase in [Ca2+]i, which was inhibited by removal of extracellular Ca2+ and by SKF96365, an inhibitor of receptor-operated Ca2+ channels. When three different soluble (1-3)-beta-glucans, with molecular weights of approximately 11,000, 150,000, and 1,000,000 Da, were tested alone for effects on Ca2+ responses, the low molecular weight (1-3)-beta-glucan produced no effect and the intermediate and high molecular weight (1-3)-beta-glucans caused only a small increase in [Ca2+]i. Interestingly, however, all three soluble (1-3)-beta-glucans could significantly reduce the Ca2+ responses induced by a subsequent exposure to either WGPs or zymosan. These results demonstrate that: 1) particulate (1-3)-beta-glucan activates Ca2+ influx in NR8383 macrophages through receptor-operated Ca2+ channels; 2) soluble (1-3)-beta-glucans do not strongly activate Ca2+ influx in these cells; and 3) soluble (1-3)-beta-glucans significantly inhibit Ca2+ influx induced by WGPs or zymosan. Soluble (1-3)-beta-glucans are likely to prevent Ca2+ influx by competitively binding to the (1-3)-beta-glucan receptors recognizing zymosan and WGPs. The smaller Ca2+ influx induced by soluble (1-3)-beta-glucans may represent only a partial activation of post-receptor signal transduction pathways necessary for inducing Ca2+ influx.
Mörk
A C
AC
Department of Pediatrics, University of Texas Health Science Center at San Antonio, 78284, USA.
Helmke
R J
RJ
Martinez
J R
JR
Michalek
M T
MT
Patchen
M L
ML
Zhang
G H
GH
D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005936:Glucans / Q000737:chemistry / Q000494:pharmacology*; D007155:Immunologic Factors / Q000494:pharmacology*; D016676:Macrophages, Alveolar / Q000187:drug effects* / Q000378:metabolism; D008970:Molecular Weight; D010316:Particle Size; D010587:Phagocytosis; D051381:Rats; D011971:Receptors, Immunologic / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D012995:Solubility; D015054:Zymosan / Q000494:pharmacology; D047071:beta-Glucans
D000276:Adjuvants, Immunologic; D000890:Anti-Infective Agents; D015220:Calcium Channels; D005936:Glucans; D007155:Immunologic Factors; D011971:Receptors, Immunologic; D047071:beta-Glucans; C045268:beta-glucan receptor; D015054:Zymosan; C033363:beta-1,3-glucan; D002118:Calcium