Is the Ca2+-sensitive K+ channel under metabolic control in human red cells?

It is widely known that a rise in internal Ca2+ leads to an increased K+ permeability of human red blood cells [1,2,3]. Binding of Ca2+ to some membrane receptors is required for the opening of the K+ channel [4]. This requirement, however, seems to alter after "ageing" red cells in vitro in acid-citrate-dextrose solutions. Thus, the free Ca2+ concentration producing half-maximal effect on K+ permeability ([Ca2+]K+-50) of 4-weeks stored cells is approx. 2.10(-4) M (calculated from ref. 3 using 50% free Ca2+ according to Schatzmann [5]); nearly ten times lower than that reported for fresh cells [6]. This observation suggests the possibility that the K+ channel may become more sensitive to Ca2+ on cold storage. The experiments described below support this idea.