Differentiation of BC3H1 smooth muscle cells changes the bivalent cation selectivity of the capacitative Ca2+ entry pathway.
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 microM) 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 (t1/2 = 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 BC3Hl 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.
Broad
L M
LM
Neuroscience Group, Faculty of Medicine and Health Sciences, University of Newcastle, NSW, Australia.
Powis
D A
DA
Taylor
C W
CW
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002413:Cations, Divalent / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006632:Histamine / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000378:metabolism; D051379:Mice; D009130:Muscle, Smooth; D015398:Signal Transduction / Q000187:drug effects; D013379:Substrate Specificity; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D002413:Cations, Divalent; D004791:Enzyme Inhibitors; D013729:Terpenes; D001464:Barium; D002110:Caffeine; D008345:Manganese; D019284:Thapsigargin; D006632:Histamine; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium