EXTRACELLULAR SITE FOR ECONAZOLE-MEDIATED BLOCK OF CA2-ACTIVATED CA2+CURRENT (I-CRAC) IN T-LYMPHOCYTES( RELEASE)

1 Standard whole cell patch clamp recording techniques were used to st udy the pharmacological characteristics and site of econazole-mediated inhibition of calcium release-activated calcium current (I-crac) in t he human leukaemic T cell line, Jurkat. 2 Extracellularly applied econ azole blocked I-carc in a concentration-dependent manner (IC(50)approx imate to 14 mu M). Block developed over a relatively slow timecourse o f 30-60 s (10 mu M), and only partially reversed over minutes. 3 Econa zole dialysed from the pipette into the cytosol at concentrations rang ing from 0.1 to 30 mu M did not reduce I-carc, or quantitatively affec t I-crac block by extracellularly applied econazole. 4 A less lipophil ic quaternary iodide derivative of econazole was synthesized to retard absorption through the cell membrane. When applied extracellularly, t his compound blocked I-crac in a concentration-dependent manner with o nset kinetics comparable to econazole. 5 Results with intracellularly dialysed econazole and the quaternary econazole derivative provide con vergent evidence that econazole blocks I-crac via an extracellular int eraction. 6 The inability of intracellularly applied econazole to inhi bit I-crac argues against the notion that econazole inhibits capacitat ive Ca2+ entry pathways secondary to its known inhibitory effects on c ytochrome P-450.