Ca2+/Na+ exchanger and Na+,K+ 2Cl- cotransporter in lens fiber plasma membrane vesicles.
When the Ca(2+)-sensitive fluorescent probe, Fura-2, or the Na(+)-sensitive probe, SBFI, in their cell permeable forms or the Cl(-)-specific probe, SPQ, were incubated with plasma membrane vesicles prepared from dogfish and bovine lenses fibers, there was a selective accumulation of the ion-specific probes within the vesicles. The SBFI and Fura-2 fluorescent excitation ratios of 340 nm to 380 nm (em: 505 nm) in the presence of an outwardly-directed Na+ gradient across the vesicles membrane, indicate that the influx of Ca2+ is increased by 152.5% and 147.4% for dogfish and bovine vesicles, respectively. The Na+ influx into the vesicles is also enhanced by 154.1% for dogfish and 149.1% for bovine lens when an outwardly-directed Ca2+ was present. This stimulation is not affected when either 50 microM valinomycin, or 50 mM K+ is present. The activity of this bidirectional Ca2+/Na+ exchanger could be inhibited by 100 microM bepridil or 200 microM La3+. The entrance behaviour of Cl- as monitored by the SPQ fluorescent signal indicates that, the Cl- influx is Na(+)-dependent. The Cl- influx is stimulated 152.8% and 187.6% for dogfish and bovine lens, respectively, when an inwardly-directed Na+ gradient is present, and is further enhanced when a K+ gradient is also present. The stoichiometry of Na+ to Cl- entering the vesicles was 1:2. This Na+,K+ 2Cl- cotransporter is not affected by 20 microM valinomycin or 50 mM K+. However, the transporter is completely inhibited by 50 microM furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)
Ye
J J
JJ
Department of Physiology and Biophysics, New York University Medical Center, NY 10016.
Zadunaisky
J A
JA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004284:Dogfish; D005665:Furosemide / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D017136:Ion Transport; D007908:Lens, Crystalline / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014634:Valinomycin / Q000378:metabolism
D002712:Chlorides; D014634:Valinomycin; D005665:Furosemide; D012964:Sodium; D006861:Hydrogen Peroxide; D011188:Potassium; D002118:Calcium