Effect of Ca2+ channel blockers on passive calcium influx into resealed human red blood cell ghosts.

Abstract

Red blood cells exhibit a slow but measurable inward leak of calcium (approx. 50 μmoles per hour per litre cells), which is easily compensated by an active Ca2+ efflux fueled by a powerful plasma membrane calcium pump (Lew et al., 1982). While there is considerable information on the calcium pump mechanism at the molecular level, mostly derived from the study of the coupled Ca2+ -ATPase activity in the isolated plasma membrane (see Schatzmann, 1982), the nature of the passive Ca2+ influx mechanism, is not well understood. It is generally agreed that passive Ca2+ uptake into intact human erythrocytes occurs by a carrier-mediated passive diffusion mechanism (Ferreira and Lew, 1977; Varecka and Carafoli, 1982; Gardos et al., 1980). The influx may occur through a protein channel, as it is inhibited by various sulphydryl agents and divalent cations (Varecka et al., 1986) and other Ca channel blockers (Locher et al., 1984). The Ca2+ influx mechanism appears to proceed by the discharge of the transmembrane K+ gradient (Varecka and Carafoli, 1982), but it does not appear to be entirely the result of hyperpolarization induced by activation of the Ca2+ -activated K+ channel (Varecka et al., 1986). By contrast to the low passive Ca2+ permeability of intact erythrocytes, resealed erythrocyte “ghosts” produced by hypotonic lysis of red cells show a considerably enhanced calcium permeability (Lew and Ferreira, 1977; Porzig, 1972). Because of the high haemoglobin content of red cells, photochromic calcium dyes cannot be readily used to study Ca2+ uptake in intact cells, but such methods have been used to study passive Ca2+ uptake into resealed white erythrocyte ghosts (Yingst and Hoffman, 1978). In the present study we have examined the effects of Ca2+ channel blockers and K on the passive uptake of Ca2+ into resealed ghosts and compared the properties of the Ca influx mechanism to those in intact cells.