Faculty Bibliography

Ammonia is a bacterial metabolite which is commonly used to alter cytoplasmic and lysosomal pH of eukaryotic cells. Here we examine its effect on external N-formyl peptide receptors of human neutrophils. Ammonia does not affect the number of N-formyl peptide receptors on the cell surface, nor the association of the ligand-receptor complex with the cytoskeleton. However, ammonia causes a marked decrease in the affinity of the chemotactic peptide receptor for its ligand. The Kd of untreated cell for the chemotactic peptide was 0.65 +/- 0.06 nM, whereas that of ammonia treated cells was 1.02 +/- 0.10 nM (Mean +/- SEM, N = 6). These results suggest that ammonia can affect external as well as internal cellular components. Since ammonia is used to alter lysosomal and cytoplasmic pH, and is a metabolite of common bacterial pathogens, these results bear directly on its use in cell biology and on its potential as a virulence factor.

We examined the relationship of microtubules to the granule organization in stimulated human polymorphonuclear leukocytes (PMNs). Electron microscopic (EM) observations of critical-point-dried PMNs revealed that only a portion of the granules appeared in close association to microtubules. These closely associated granules appeared to be attached to the microtubule via smaller-diameter filaments. The remaining granules appeared either attached to microtubules at a further distance, via smaller-diameter filaments such as actin, or unassociated with microtubules. EM observations of PMNs treated with either the microtubule promoter drug taxol or the microtubule depolymerization drugs nocodozole and colchicine revealed a redistribution of granules towards the nucleus. Granule clustering at the periphery of the cell was also noted with nocodozole and colchicine. With cytochalasin B, a uniform distribution of granules was noted. However, granule clustering was noted when PMNs were coincubated with cytochalasin B and colchicine. These results indicate that microtubules may have both a direct and indirect role (through other cytoskeletal elements) in the organization of PMN granules.