CA2-ACTIVATED K+ CHANNEL AND THE ACTIVATION OF CA2+ INFLUX IN VANADATE-TREATED RED-BLOOD-CELLS()

The mechanism by which K+ inhibits vanadate-induced Ca-45(2+) influx b y human red blood cells (RBC) was studied using several independent ap proaches. The following results were found: 1. The inhibitory effect o f K+ was absent when RBC were loaded with a Ca2+-chelator. This treatm ent at the same time inhibited the vanadate-induced K+ efflux, and the membrane hyperpolarization induced by Ca2+ in vanadate-treated cells. 2. The potency of K+, Rb+, and Cs+ to inhibit vanadate-induced Ca2+ i nflux corresponded to their ability to depolarize the RBC membrane via the Ca2+-activated K+ channel (K(Ca)). 3. Inhibition of the vanadate- induced Ca-45(2+) influx by a protonophore proceeded ill parallel with the inhibition of the vanadate-plus-Ca2+-induced membrane hyperpolari zation. 4. Valinomycin in part released the inhibition of the vanadate -induced Ca2+ influx by known K(Ca) inhibitors (quinine, oligomycin, 4 -aminopyridine) but not by inhibitors of the Ca2+ channel (Cu2+, HS-re agents, organic Ca2+ channel blockers). 5. K+ did not inhibit the vana date-induced Ca2+ influx in dog RBC which have K(Ca) hut no transmembr ane K+ gradient. The inhibition of the vanadate-induced Ca2+ influx by external K+ appears to be due to the elimination of the electrical co mponent of the Ca2+-motive force imposed by opening of the K(Ca). This implies that the Ca2+ carrier mediating the influx of Ca2+ in the pre sence of vanadate is of uniport type, and that the activity of K(Ca) m ay serve as a supporting element for Ca2+ influx.