Journal Article

Transmembrane signalling in human monocyte/mesangial cell co‐cultures: role of cytosolic Ca<sup>2+</sup>

Paolo Menè, Francescaromana Festuccia, Rosaria Polci, Francesco Pugliese and Giulio A. Cinotti

in Nephrology Dialysis Transplantation

Published on behalf of European Renal Association - European Dialysis and Transplant Assoc

Volume 17, issue 1, pages 42-49
Published in print January 2002 | ISSN: 0931-0509
Published online January 2002 | e-ISSN: 1460-2385 | DOI: http://dx.doi.org/10.1093/ndt/17.1.42
Transmembrane signalling in human monocyte/mesangial cell co‐cultures: role of cytosolic Ca2+

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Background. Adhesion of monocytes triggers apoptosis, cytotoxicity, cytokine release, and later proliferation of cultured human mesangial cells (HMC). In the search for transmembrane signals transducing the interaction of HMC adhesion molecules with leukocyte counterreceptors, we measured variations of cytosolic Ca2+ ([Ca2+]i) in HMC and monocytes of the U937 cell line during 6‐h co‐cultures.

Methods. Monolayer cultures of HMC and suspensions of U937 cells were loaded with the fluoroprobe fura 2‐AM and subsequently co‐cultured for 6 h while separately monitoring by microfluorometry the Ca2+‐dependent 500 nm fluorescent emission of each cell line at fixed intervals upon excitation at 340/380 nm.

Results. U937 and peripheral blood monocyte adhesion was followed in HMC by a slow, progressive rise of [Ca2+]i from basal levels of 96±9 nM to 339±54 at 60 min and 439±44 nM at 3 h. The [Ca2+]i elevation reached a steady state thereafter, while parallel monolayers incubated with control media maintained resting levels throughout the co‐culture with stable fluoroprobe retention. Receptor sensitivity to vasoconstrictor agents, including compounds not released by monocytes, such as angiotensin II, was rapidly downregulated in HMC co‐cultured with U937 cells. No [Ca2+]i changes could be elicited by the octapeptide or by the TxA2 analogue, U‐46619, as early as 30 min after exposure to U937 cells. No [Ca2+]i changes were observed in U937 cells throughout the co‐culture. Conditioned media from monocytes and from co‐cultured HMC+U937 cells had no effect on [Ca2+]i of HMC. Ca2+ entry leading to fura 2 saturation was still inducible by Ca2+ ionophores, such as ionomycin and 4‐Br‐A23187, which also inhibited the responses to vasoconstrictors. Ca2+‐free solutions prevented the [Ca2+]i rise as well as subsequent receptor inactivation, implicating Ca2+ influx through store‐operated Ca2+ channels (SOC), a major pathway for Ca2+ entry in these cultured cells. Ca2+ influx was confirmed by Mn2+‐quenching of fura 2.

Conclusions. In HMC, early changes in [Ca2+]i signal for monocyte adhesion in a co‐culture model of glomerular inflammation. This signalling mechanism may mediate the functional responses elicited in glomerular cells by leukocytes, including downregulation of receptors for vasoactive agents.

Keywords: Ca2+ channels; cytosolic free Ca2+; mesangium; monocytes; signalling

Journal Article.  5455 words.  Illustrated.

Subjects: Nephrology

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