Study on calcium transport by sarcoplasmic reticulum vesicles using fluorescence probes.

Fluorescence changes of 1-anilino-8-naphthalenesulfonic acid and 3,3'-dipropyl-2,2'-thiadicarbocyanine during Ca transport by sarcoplasmic reticulum vesicles were studied. The fluorescence of both probes is enhanced corresponding to the rapid initial Ca uptake. The enhancement could be interpreted in terms of increased binding of the former (anionic) dye and decreased binding of the latter (cationic) dye to the vesicles, suggesting a change in the surface charge of the membranes associated with Ca transport. Under limited conditions where Na, K, and Mg were not added exogenously, Ca could be transported without concomitant counter-transport of these cations.