Differentiation of the human monocytic cell line U937 results in an upregulation of the calcium release-activated current, ICRAC.
1. Single cell fura-2 fluorescence measurements and whole-cell patch clamp recordings were used to investigate the effects of macrophage-like differentiation, induced by dibutyryl cAMP (dbcAMP), on Ca2+ influx triggered by Ca2+ store depletion in the human monocytic cell line, U937. 2. In differentiated cells, the rise in intracellular [Ca2+] following store depletion by thapsigargin (TG) in nominally Ca(2+)-free solution was 94% greater and the [Ca2+]i rise on subsequent re-addition of external Ca2+ (2 mM) was 292% greater than in undifferentiated cells. 3. Under conditions where [Ca2+]i was buffered by BAPTA, TG-induced store depletion failed to activate a detectable inward Ca2+ current in undifferentiated U937 cells. Under identical conditions, store depletion of differentiated U937 cells generated an inwardly rectifying Ca(2+)-selective current which showed no reversal from -140 to +30 mV and was blocked by 1 microM external La3+; characteristics of the calcium release-activated Ca2+ current (ICRAC) identified in other cells. 4. We conclude that U937 cells show a differentiation-dependent upregulation of a store-mediated Ca2+ entry pathway, identified as ICRAC, which is not correlated with the small associated increase in the size of TG-sensitive Ca2+ pools.
Physiological Laboratory, University of Cambridge, UK. af@mole.bio.cam.ac.uk
R A
RA
Floto
M P
MP
Mahaut-Smith
J M
JM
Allen
B
B
Somasundaram
D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007202:Indicators and Reagents; D008564:Membrane Potentials / Q000502:physiology; D009000:Monocytes / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D019284:Thapsigargin / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D003994:Bucladesine; D019284:Thapsigargin; D002118:Calcium; D016257:Fura-2