Properties of the CA2+-activated K+ conductance of human red cells as revealed by the patch-clamp technique.
Application of Ca2+ to the inner surface of red-cell membranes activates unitary currents that can be measured in cell-attached and cell-free membrane patches. Ca2+ can be replaced by Pb2+ to activate the single channels. In addition to internal Ca2+ external K+ has to be present. The channels are preferentially permeable to K+ with a selectivity ratio PK:PNa of about 15:1 as estimated from measurement of reversal potentials. The dependence of channel activity on Ca2+ is compatible with the conception that the binding of two Ca2+ is necessary to open a single channel. Both the channel activity and the single-channel conductance exhibit inward rectification. External and internal Na+ inhibit the K+ currents. The reported results suggest that the unitary current events are responsible for the Ca2+-dependent K+ permeability known from measurement on cell suspensions. Therefore, comparison of the two techniques allows calculation of the number of K+ channels per red cell, which on average is about 10.
D002118:Calcium / Q000097:blood*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007473:Ion Channels / Q000378:metabolism*; D007854:Lead / Q000494:pharmacology; D008433:Mathematics; D008564:Membrane Potentials; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood; D013997:Time Factors
D007473:Ion Channels; D007854:Lead; D012964:Sodium; D011188:Potassium; D002118:Calcium