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. 1977 Aug;269(3):707–722.1. doi: 10.1113/jphysiol.1977.sp011924

Effects of injections of calcium and EGTA into the outer segments of retinal rods of Bufo marinus

J E Brown 1,2,3, J A Coles 1,2,3, L H Pinto 1,2,3,*
PMCID: PMC1283735  PMID: 408483

Abstract

1. Intracellular recordings were made from the outer segments of rods in the isolated, superfused retina of Bufo marinus. Cells were impaled under observation with a compound microscope fitted with an infra-red image converter. Changes of membrane voltage and some concomitant changes of input resistance were measured in response to light, membrane polarization and iontophoretic injections.

2. By means of a double barrel micropipette, charge was passed into a rod from a micropipette barrel that contained Ca2+ while no net current crossed the plasma membrane. In about half the cells, immediately after the injection, a hyperpolarization was observed that decayed with a time course similar to the decay of the receptor potential.

3. Membrane hyperpolarization also occurred after a depolarizing current stopped flowing into a rod through a single barrel pipette that contained only K-acetate. This hyperpolarization was accompanied by an increase of membrane conductance. The reversal potential for the conductance-increase was between the voltage in the dark and the voltage in the absence of [Na+]out. A larger hyperpolarization became evident after an equal depolarizing current stopped flowing into a rod through a pipette that also contained Ca2+; this larger after-hyperpolarization was due to both the cessation of depolarizing current and the injection of Ca2+.

4. A depolarization of 10-20 mV that lasted 2-60 sec became evident after hyperpolarizing current stopped flowing into a rod through a single-barrel pipette filled with K-EGTA. During the after-depolarization, the responses to small, dim spots of light were attenuated. No depolarization was observed after passing hyperpolarizing currents into rods through pipettes that contained either acetate-, SO2-4 or MOPS-.

5. These results show that sequestration of [Ca2+]in depolarizes the plasma membrane and that an increase in [Ca2+]in hyperpolarizes the membrane mimicking the later part of the receptor potential. These findings support the hypothesis of Yoshikami & Hagins (1971) that Ca2+ is an intracellular messenger for excitation in vertebrate rods.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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