title: An estimate of the number of Ca2+-dependent K+ channels in the human red cell.
abstract: An original approach has been designed to count Ca2+-dependent K+ channels in the human red cell using a preparation of inside-out vesicles. The relative frequency of vesicles having no K+ channels is estimated from the fraction of 42K+ (or 86Rb+) which is not released from loaded vesicles on maximal stimulation with Ca2+. The mean number of channels per vesicle is then calculated from this figure assuming a Poisson distribution for the K+ channels. From this value and the mean vesicular radius, computed from the volume/surface ratio, the mean number of channels per cell can be estimated. A value of 142 +/- 27 (mean +/- S.E.) was obtained, which is well above that estimated by comparison of unitary conductance and tracer equilibration rate measurements (about 10 channels/cell, Grygorczyk, R. Schwarz, W. and Passow, H. (1984) Biophys. J. 45, 693-698), but compares favourably with the channel density inferred from comparison with the number of Na+ pumps in a similar preparation of inside-out vesicles (100-200/cell, Lew, V.L., Muallem, S. and Seymour, C.A. (1982) Nature 296, 742-744). The procedure described here can be considered for general application as an alternative to other known procedures.
mesh_terms: D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D004910:Erythrocyte Membrane / Q000032:analysis* / Q000648:ultrastructure; D006801:Humans; D007473:Ion Channels / Q000032:analysis* / Q000187:drug effects; D007700:Kinetics; D008081:Liposomes / Q000032:analysis; D010316:Particle Size; D011188:Potassium / Q000097:blood*; D012414:Rubidium Radioisotopes; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D008081:Liposomes; D012414:Rubidium Radioisotopes; D014634:Valinomycin; D000001:Calcimycin; D011188:Potassium; D002118:Calcium