Coupling between transmembrane calcium transport and membrane potential in retinal rod discs.
Changes in the transmembrane potential of bovine rod discs were studied by use of the potential-sensitive fluorescence probes diS-C3-(5) and diBA-C4-(5). The disc membrane was shown to be impermeable to potassium ions. Their concentration in the disc is as high as 2.1 +/- 0.3 mM. The permeability of the disc membrane to Ca2+ was shown to be selective. The accumulation and release of Ca2+ were found to be accompanied by the generation of inside positive and inside negative transmembrane potentials, respectively. The uptake of Ca2+ in the discs may operate against the concentration gradient of the ion. The value of the potential developed is directly proportional to the logarithm of free Ca2+ concentration in the medium (delta phi m = 11.2 +/- 1.6 mV at 4.85 microM Ca2+fr). The accumulation of Ca2+ is decreased by sodium ions and totally inhibited by monensin. This indicates that a Na-Ca exchange process participates in Ca2+ uptake of photoreceptor discs.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000502:physiology; D003624:Darkness; D005456:Fluorescent Dyes; D007700:Kinetics; D008564:Membrane Potentials; D010786:Photoreceptor Cells / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000502:physiology*; D013816:Thermodynamics
D005456:Fluorescent Dyes; D002118:Calcium