ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Because the level of extracellular Ca2+ is an important stimulus for differentiation of epidermal cells in vitro, we characterized the extracellular Ca2+ -dependent transmembrane Ca2+ fluxes in BALB/MK mouse keratinocytes. Increasing levels of extracellular Ca2+ ranging from 0.07 to 1.87 mM, stimulated the rate of 45Ca2+ uptake into these cells 10- to 70-fold and doubled the rate of 45Ca2+ efflux. The divalent cations, Ni2+ and Co2+, were able to block the influx of Ca2+, but dihydropyridines and verapamil were not. Furthermore, 10 to 100 μM of the trivalent cation La3+ induced a dose-dependent 2- to 100-fold increase of Ca2+ uptake, independently of the level of extracellular Ca2+. These observations suggest that keratinocytes possess a cell-surface “Ca2+ -receptor,” activation of which stimulates the influx of 45Ca2+ through a type of voltage-independent, receptor-operated Ca2+ channels. Epidermal growth factor induced an accumulation of 45Ca2+ of a much smaller magnitude than elevations of the level of extracellular Ca2+, without a detectable increase of Ca2+ efflux. Thus, the divergent cellular responses of keratinocytes to EGF and extracellular Ca2+ may be due, in part, to the distinct changes in transmembrane Ca2+ fluxes that these two stimuli generate. Treatment of cells with type β transforming growth factor led to a gradual 6-fold increase of the Ca2+ -activated rate of Ca2+ uptake over a period of 4 hours, but reduced the Ca2+ efflux by approximately 50% within 10 minutes. Thus, type β transforming growth factor apparently stimulates Ca2+ influx indirectly, but may control the differentiation of keratinocytes by direct inhibition of Ca2+ efflux pumps.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041470213
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