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  • Title: Effects of injections of calcium and EGTA into the outer segments of retinal rods of Bufo marinus.
    Author: Brown JE, Coles JA, Pinto LH.
    Journal: J Physiol; 1977 Aug; 269(3):707-22. PubMed ID: 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 Ca(2+) 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 Ca(2+); this larger after-hyperpolarization was due to both the cessation of depolarizing current and the injection of Ca(2+).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(-), SO(2-) (4) or MOPS(-).5. These results show that sequestration of [Ca(2+)](in) depolarizes the plasma membrane and that an increase in [Ca(2+)](in) hyperpolarizes the membrane mimicking the later part of the receptor potential. These findings support the hypothesis of Yoshikami & Hagins (1971) that Ca(2+) is an intracellular messenger for excitation in vertebrate rods.
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