title: Evidence for membrane potential changes in isolated synaptic membrane ghosts monitored with a merocyanine dye.
abstract: Changes in the fluorescence intensity of merocyanine-540 were measured in suspensions of synaptic plasma membrane ghosts isolated from rat brain cortex. With preincubation of the membrane ghosts in isotonic KCl or NaCl solution, K- and Na-enriched ghosts samples were prepared. In suspensions of both sort of synaptic membrane ghosts, merocyanine-540 showed a fluorescnece emission peak at a wavelength of 590 nm. Under a fixed total concentration of NaCl and KCl, high external K+ induced an increase in the fluorescence intensity, such an increase being proportional to logarithm of K+ concentration. Replacing K+ by Rb+, NH4+ or Cs+, a similar effect was observed. Rb+ was about as effective as K+ ; NH4 is about 2/3 and Cs+ 1/4 as effective. But the changes in fluorescence with increasing K+ concentration were larger in K-ghosts than in Na-ghosts. K+-induced fluorescence changes were very small when gramicidin D was added to the suspension. K+-induced fluorescence changes were not observed in ultrasonicated ghost suspensions. Such findings seem to indicates that the K+-ions induced fluorescence increase reflect the depolarization in the isolated synaptic plasma membrane ghosts. Furthermore, the permeability ratio PNa/PK (PNa, PK: the permeability constant for Na+ and K+) was estimated to be smaller than 0.03.
mesh_terms: D000818:Animals; D001583:Benzoxazoles; D002458:Cell Fractionation; D002540:Cerebral Cortex / Q000166:cytology; D005453:Fluorescence; D005456:Fluorescent Dyes; D006096:Gramicidin / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology; D011744:Pyrimidinones; D051381:Rats; D013570:Synaptic Membranes / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D001583:Benzoxazoles; D005456:Fluorescent Dyes; D011744:Pyrimidinones; D006096:Gramicidin; C003954:merocyanine dye; D011188:Potassium