Monovalent cation permeability and Ca(2+) block of the store-operated Ca(2+) current I(CRAC )in rat basophilic leukemia cells.
Like voltage-operated Ca(2+) channels, store-operated CRAC channels become permeable to monovalent cations in the absence of external divalent cations. Using the whole-cell patch-clamp technique, we have characterized the permeation and selectivity properties of store-operated channels in the rat basophilic leukemia (RBL-1) cell line. Store depletion by dialysis with InsP(3) and 10 mM EGTA resulted in the rapid development of large inward currents in Na(+)- and Li(+)-based divalent-free solutions. Cs(+) permeated the channels poorly (P(Cs)/ P(Na)=0.01). Trimethylamine (TMA(+)), tetramethylammonium (TeMA(+)), tetraethylammonium (TEA(+)), N-methyl- D-glucamine (NMDG(+)) and TRIS(+) were not measurably permeant. NH(4)(+) was conducted well. We estimated the minimum pore diameter under divalent-free conditions to be between 0.32 nm and 0.55 nm. When cells were dialysed with buffered Ca(2+) solution and I(CRAC) activated by application of thapsigargin, P(Cs)/ P(Na) was still low (0.08). Outward currents through CRAC channels were carried by intracellular Na(+), K(+) and, to a much lesser extent, by Cs(+). Currents were unaffected by dialysis with Mg(2+)-free solution. The Na(+) current was inhibited by external Ca(2+) (half-maximal blocking concentration of 10 microM). This Ca(2+)-dependent block could be alleviated by hyperpolarization. The monovalent Na(+) current was voltage dependent, increasing as the holding potential depolarized above 0 mV. Our results suggest that CRAC channels in RBL-1 cells have a smaller pore diameter than voltage-operated Ca(2+) channels, discriminate between Group I cations, and differ markedly in their selectivity from CRAC channels reported in lymphocytes.
Bakowski
Daniel
D
Laboratory of Cellular and Molecular Signalling, Department of Physiology, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
Parekh
Anant B
AB
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002414:Cations, Monovalent / Q000493:pharmacokinetics; D002586:Cesium / Q000493:pharmacokinetics; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D015471:Leukemia, Basophilic, Acute; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D051381:Rats; D012964:Sodium / Q000493:pharmacokinetics; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D002414:Cations, Monovalent; D002586:Cesium; D012964:Sodium; D008274:Magnesium; D002118:Calcium