Affiliation:
1. Department of Pharmacology, Tennis Court Road, Cambridge CB2 1QJ, U.K.
2. Neuroscience Group, Faculty of Medicine and Health Sciences, The University of Newcastle, Newcastle, NSW 2308, Australia
Abstract
Differentiation of BC3H1 cells leads to expression of a variety of proteins characteristic of smooth muscle and to changes in the behaviour of intracellular Ca2+ stores. Treatment of both differentiated and undifferentiated cells with thapsigargin (2 μM) emptied their intracellular Ca2+ stores, and in the presence of extracellular Ca2+ caused an increase in cytosolic [Ca2+] that rapidly reversed after its removal. The amplitudes of these capacitative Ca2+ entry signals were 101±8 nM (n = 42) in differentiated cells and 188±16 nM (n = 35) in undifferentiated cells. Mn2+ entry in thapsigargin-treated cells, measured by recording the quenching of cytosolic fura 2 fluorescence, was 374±26% (n = 34) and 154±7% (n = 41) of control rates in differentiated and undifferentiated cells, respectively. Empty stores caused Ba2+ entry to increase to 282±20% (n = 8) of its basal rate in differentiated cells and to 187±20% (n = 8) in undifferentiated cells. Rates of Ca2+ extrusion, measured after rapid removal of extracellular Ca2+ from cells in which capacitative Ca2+ entry had been activated, were similar in differentiated (t½ = 23±2 s, n = 7) and undifferentiated (23±1 s, n = 6) cells. The different relationships between capacitative Ca2+ and Mn2+ signals are not, therefore, a consequence of more active Ca2+ extrusion mechanisms in differentiated cells, nor are they a consequence of different fura 2 loadings in the two cell types. We conclude that during differentiation of BC3H1 cells, the cation selectivity of the capacitative pathway changes, becoming relatively more permeable to Mn2+ and Ba2+. The change may result either from expression of a different capacitative pathway or from modification of the permeation properties of a single pathway.
Subject
Cell Biology,Molecular Biology,Biochemistry
Cited by
17 articles.
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