Extracellular site for econazole-mediated block of Ca2+ release-activated Ca2+ current (Icrac) in T lymphocytes

1. Standard whole cell patch clamp recording techniques were used to study the pharmacological characteristics and site of econazole-mediated inhibition of calcium release-activated calcium current (Icrac) in the human leukaemic T cell line, Jurkat. 2. Extracellularly applied econazole blocked Icrac in a concentration-dependent manner (IC50 approximately 14 microM). Block developed over a relatively slow timecourse of 30-60 s (10 microM), and only partially reversed over minutes. 3. Econazole dialysed from the pipette into the cytosol at concentrations ranging from 0.1 to 30 microM did not reduce Icrac, or quantitatively affect Icrac block by extracellularly applied econazole. 4. A less lipophilic quaternary iodide derivative of econazole was synthesized to retard absorption through the cell membrane. When applied extracellularly, this compound blocked Icrac in a concentration-dependent manner with onset kinetics comparable to econazole. 5. Results with intracellularly dialysed econazole and the quaternary econazole derivative provide convergent evidence that econazole blocks Icrac via an extracellular interaction. 6. The inability of intracellularly applied econazole to inhibit Icrac argues against the notion that econazole inhibits capacitative Ca2+ entry pathways secondary to its known inhibitory effects on cytochrome P-450.