Divalent ion trapping inside potassium channels of human T lymphocytes.
Using the patch-clamp whole-cell recording technique, we investigated the influence of external Ca2+, Ba2+, K+, Rb+, and internal Ca2+ on the rate of K+ channel inactivation in the human T lymphocyte-derived cell line, Jurkat E6-1. Raising external Ca2+ or Ba2+, or reducing external K+, accelerated the rate of the K+ current decay during a depolarizing voltage pulse. External Ba2+ also produced a use-dependent block of the K+ channels by entering the open channel and becoming trapped inside. Raising internal Ca2+ accelerated inactivation at lower concentrations than external Ca2+, but increasing the Ca2+ buffering with BAPTA did not affect inactivation. Raising [K+]o or adding Rb+ slowed inactivation by competing with divalent ions. External Rb+ also produced a use-dependent removal of block of K+ channels loaded with Ba2+ or Ca2+. From the removal of this block we found that under normal conditions approximately 25% of the channels were loaded with Ca2+, whereas under conditions with 10 microM internal Ca2+ the proportion of channels loaded with Ca2+ increased to approximately 50%. Removing all the divalent cations from the external and internal solution resulted in the induction of a non-selective, voltage-independent conductance. We conclude that Ca2+ ions from the outside or the inside can bind to a site at the K+ channel and thereby block the channel or accelerate inactivation.
Grissmer
S
S
Department of Physiology and Biophysics, University of California, Irvine 92717.
Cahalan
M D
MD
D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D008274:Magnesium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism*; D013997:Time Factors
D002413:Cations, Divalent; D015221:Potassium Channels; D001464:Barium; D012964:Sodium; D008274:Magnesium; D012413:Rubidium; D011188:Potassium; D002118:Calcium