CDNA CLONING AND FUNCTIONAL-CHARACTERIZATION OF THE MOUSE CA2-GATED K+ CHANNEL, MIK1 - ROLES IN REGULATORY VOLUME DECREASE AND ERYTHROID DIFFERENTIATION()

We have cloned from murine erythroleukemia (MEL) cells, thymus, and st omach the cDNA encoding the Ca2+-gated K+ (K-Ca) channel, mIK1, the mo use homolog of hIK1 (Ishii, T. M., Silvia, C., Hirschberg, B., Bond, C . T., Adelman, J. P., and Maylie, J. (1997) Proc. Natl. Acad. Sci.(U. S. A. 94, 11651-11656), mIK1 mRNA was detected at varied levels in man y tissue types. mIK1 K-Ca channel activity expressed in Xenopus oocyte s closely resembled the K-Ca of red cells (Grardos channel) and MEL ce lls in its single channel conductance, lack of voltage-sensitivity of activation, inward rectification, and Ca2+ concentration dependence. m IK1 also resembled the erythroid channel in its pharmacological proper ties, mediating whole cell and unitary currents sensitive to low nM co ncentrations of both clotrimazole (CLT) and its des-imidazolyl metabol ite, 2-chlorophenyl-bisphenyl-methanol, and to low nM concentrations o f iodocharybdotoxin, Whereas control oocytes subjected to hypotonic sw elling remained swollen, mIK1 expression conferred on oocytes a novel, Ca2+-dependent, CLT-sensitive regulatory volume decrease response. Hy potonic swelling of voltage-clamped mIK1-expressing oocytes increased outward currents that were Ca2+-dependent, CLT-sensitive, and reversed near the K+ equilibrium potential. mIK1 mRNA levels in ES cells incre ased steadily during erythroid differentiation in culture, in contrast to other K-Ca mRNAs examined. Low nanomolar concentrations of CLT inh ibited proliferation and erythroid differentiation of peripheral blood stem cells in Liquid culture.