Evidence for direct involvement of the sarcoplasmic reticulum Ca²⁺‐ATPase in a passive monovalent cation (K⁺/Na⁺) exchange

DOI:

10.1016/0014-5793(95)01267-1

Authors:

Florence de Jesus, Martine Cuillel, Yves Dupont

Abstract:

A specific inhibitor of SERCA-pumps, thapsigargin (TG) was used to demonstrate the direct involvement of the SR Ca(2+)-ATPase in passive K+/Na+ exchange. The K(+)-potential variations across vesicle membranes were measured in the absence of ATP with a fluorescent probe: 3,3′-dipropylthiodicarbocyanine iodide. Addition of EGTA dissipates the K(+)-potential whereas the presence of TG abolishes this effect. Our data prove that the Ca(2+)-ATPase translocates monovalent cations at a rate similar to the E2–>E1 conformational change.