Properties of the Ca2+-activated K+ channel in one-step inside-out vesicles from human red cell membranes

• Published in: Nature (London) 1982-04, Vol.296 (5859), p.742-744
• Main Authors: Lew, Virgilio L., Muallem, Shmuel, Seymour, Carol A.
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - pharmacology; Calcium - blood; Cell-Free System; Edetic Acid - pharmacology; Erythrocyte Membrane - physiology; Erythrocytes - physiology; Humanities and Social Sciences; Hydrogen-Ion Concentration; Ion Channels - physiology; letter; multidisciplinary; Potassium - blood; Rubidium; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/296742a0

The presence of a calcium-activated potassium channel in some mammalian red cell membranes makes them useful experimental models in which to study the properties of similar mechanisms believed to be involved in the control of membrane potential and conductance, at rest and during activity, in many other cells. However, vesicles prepared from human red cell membranes by the method of Steck et al. 1 , whether inside-out (IOVs) or right-side out (ROVs), either failed to show any Ca 2+ -activated component of K + (Rb + ) fluxes 2 or showed only a very reduced calcium sensitivity and K + /Na + selectivity 3 . This is surprising because there is good functional preservation of other transport mechanisms, such as the anion carrier 4 , Ca 2+ pump 5 and Na + pump 6 . Our failure to confirm reports 7 that the calcium response could be restored in ‘silent’ IOVs by addition of protein concentrates from red cell lysates prompted the search for and discovery of vesiculation procedures which produced ion-tight IOVs in a single step, with minimum loss of membrane components and transport properties 8–11 . We report here (1) the conditions which favour preservation or loss of the Ca 2+ -activated component of the 86 Rb efflux from one-step IOVs, (2) an approximate estimate of the number of Ca 2+ -activated K + channels per red cell, and (3) that individual Ca 2+ -activated K + channels respond in an all or nothing fashion to Ca 2+ activation and differ in their threshold sensitivity to ionized calcium.