Abstract
Changes in the transmembrane potential of bovine rod discs were studied by use of the potential-sensitive fluorescence probes diS-C
3
-(5) and diBA-C
4
-(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 Ca
2+
was shown to be selective. The accumulation and release of Ca
2+
were found to be accompanied by the generation of inside positive and inside negative transmembrane potentials, respectively. The uptake of Ca
2+
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 Ca
2+
concentration in the medium (Δφ
m
=11.2 ± 1.6 mV at 4.85 μM Ca
2+
fr
). The accumulation of Ca
2+
is decreased by sodium ions and totally inhibited by monensin. This indicates that a Na-Ca exchange process participates in Ca
2+
uptake of photoreceptor discs.
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