Activation of Ca2+ current in Jurkat T cells following the depletion of Ca2+ stores by microsomal Ca(2+)-ATPase inhibitors.
The mechanism of TCR-stimulated Ca2+ influx was studied in the Jurkat human T cell line using Ca2+ indicator dyes and whole-cell patch clamp. Ca2+ influx induced by inositol 1,4,5-triphosphate (IP3)-coupled surface receptors (either the TCR or a heterologous muscarinic receptor) was compared with Ca2+ influx induced by inhibitors of the microsomal Ca(2+)-ATPase (thapsigargin, cyclopiazonic acid, di-tert-butylhydroquinone), which release stored Ca2+ without production of IP3. The same Ca2+ influx pathway could be activated by IP3-dependent or IP3-independent means, and therefore appeared to be regulated by the fullness of the microsomal Ca2+ stores rather than by the direct action of IP3. Depletion of stored Ca2+ by either receptor stimulation or microsomal Ca(2+)-ATPase inhibition activated a low conductance, Ca(2+)-selective, non-voltage-activated membrane current. Ca2+ currents induced by receptor stimulation and Ca(2+)-ATPase inhibition were not additive. Several properties of the depletion-activated Ca2+ current suggest that it is carried by a novel type of Ca2+ channel rather than an electrogenic carrier or pump. The conductance saturated when external Ca2+ was raised (Kd approximately 2 mM) and became highly permeable to monovalent cations when external Ca2+ was lowered to below 100 nM, much as has been observed for some voltage-gated Ca2+ channels. The Ca2+ current was reversibly blocked by > 90% with 0.3 mM Cd2+, whereas the same concentration of Ni2+ or Co2+ blocked only 50 to 60% of the current. However, the absence of voltage-dependent activation, relative conductance sequence for divalent cations (Ca2+ > Ba2+ approximately Sr2+ >> Mn2+), and lack of inhibition by nifedipine, D600, diltiazem, delta-conotoxin, or aga-IVa were unlike that of voltage-gated Ca2+ channels.
Premack
B A
BA
Department of Molecular Pharmacology, Stanford University School of Medicine, CA 94305.
McDonald
T V
TV
Gardner
P
P
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002478:Cells, Cultured; D005470:Fluorometry; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D008861:Microsomes / Q000201:enzymology; D013601:T-Lymphocytes / Q000378:metabolism*
D015220:Calcium Channels; D015544:Inositol 1,4,5-Trisphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium