PubMed · 14461335
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C LABROUSSE. 1961. [Calcemia].. https://pubmed.ncbi.nlm.nih.gov/14461335/
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This study was designed to investigate the possible involvement of NADPH oxidase and the Na(+)/Ca(2+) exchanger in regulating membrane repolarisation and store-operated uptake of Ca(2+) by FMLP (1 microM)-activated human neutrophils. Diphenyleneiodonium chloride (DPI, 5-10 microM) and KB-R7943 (2.5-10 microM), inhibitors of NADPH oxidase and the reverse mode of the Na(+)/Ca(2+) exchanger respectively, were used as pharmacological probes. Transmembrane fluxes of Ca(2+), K(+) and Na(+) were determined radiometrically, while alterations in membrane potential and cytosolic Ca(2+) were evaluated using spectrofluorimetric procedures. DPI, added to the cells at the time of maximum FMLP-activated membrane depolarisation, accelerated the rates of both membrane repolarisation and influx of Ca(2+), while KB-R7943 effectively antagonised these processes. SKF 96365 (10 microM), an antagonist of store-operated Ca(2+) channels, abolished the influx of Ca(2+) into FMLP-activated neutrophils, but had no effects on membrane repolarisation, suggesting that the Na(+)/Ca(2+) exchanger is primarily involved in mediating membrane repolarisation, thereby facilitating uptake of Ca(2+) via store-operated channels. These observations are compatible with prominent negative and positive regulatory roles for NADPH oxidase and the Na(+)/Ca(2+) exchanger respectively in regulating the rates of membrane repolarisation and store-operated uptake of Ca(2+) by chemoattractant-activated neutrophils.
The agent hemin has been demonstrated to be able to initiate a coordinated differentiation program in several cell types. In the present study, we examined the ability of hemin on inducing cell differentiation and Ca(2+)-activated K(+) channel activity in erythroleukemic K562 cells. Treating undifferentiated K562 cells with hemin (0.1 mM) for five days caused these cells to display differentiation-like characteristics including chromatin aggregation, nuclear degradation, pseudopod extension of the membrane and increased hemoglobin production. However, overall cell viability was not significantly changed by the presence of hemin. After hemin treatment for different periods, the Ca(2+)-activated K(+) channel was activated by the addition of ionomycin (1 microM), and was inhibited by either clotrimazole, charybdotoxin, or EGTA. Before hemin treatment there was no significant Ca(2+)-activated K(+) channel activity present in undifferentiated K562 cells. After hemin treatment for 5 days, a significant Ca(2+)-activated K(+) channel activity was detected. This increasing Ca(2+)-activated K(+) channel activity may be contributed from a subtype of Ca(2+)-activated K(+) channel, KCNN4. These results suggest that the ability of hemin to induce increasing Ca(2+)-activated K(+) channel activity may contribute to the mechanism of hemin-induced K562 cell differentiation.
The epidermis is the largest organ in the body. It is comprised primarily of keratinocytes which are arranged in layers that recapitulates their programmed life cycle. Proliferating keratinocytes are on the bottom-the stratum basale. As keratinocytes leave the stratum basale they begin to differentiate, culminating in the enucleated stratum corneum which has the major role of permeability barrier. Calcium and the active metabolite of vitamin D, 1,25(OH)(2)D(3), play important roles in this differentiation process. The epidermis has a gradient of calcium with lowest concentrations in the stratum basale, and highest concentrations in the stratum granulosum where proteins critical for barrier function are produced. Vitamin D is made in different layers of the epidermis, but 1,25(OH)(2)D(3) is made primarily in the stratum basale. Together calcium and 1,25(OH)(2)D(3) regulate the ordered differentiation process by the sequential turning on and off the genes producing the elements required for differentiation as well as activating those enzymes involved in differentiation. Animal models in which the sensing mechanism for calcium, the receptor for 1,25(OH)(2)D(3), or the enzyme producing 1,25(OH)(2)D(3) have been rendered inoperative demonstrate the importance of these mechanisms for the differentiation process, although each animal model has its own phenotype. This review will examine the mechanisms by which calcium and 1,25(OH)(2)D(3) interact to control epidermal differentiation.