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L H Pinto

Publications and source records attributed to L H Pinto.

At least 73 records · Page 4Linked to original sources
PubMed1984

Pressure injection of 3',5'-cyclic GMP into solitary rod photoreceptors of the tiger salamander.

The outer segments of solitary rods of large neotenic Ambystoma tigrinum were impaled with double-barrel micropipettes. One barrel was used to record membrane voltage and the other barrel was used both to pass voltage-clamp current and to pressure-inject cyclic GMP. Injections of cyclic GMP induced inward currents in normal cells that were bathed in Ringer's solution and studied at the dark, resting voltage. These cyclic GMP-induced currents reversed sign for voltages 25-40 mV more positive than the dark, resting voltage; however, light-induced currents did not reverse sign for voltages as depolarized as 55 mV more positive than the dark, resting voltage. The responses to light became slow and very prolonged in cells that had been injected with large amounts of cyclic GMP. In these over-injected cells, both light-induced and cyclic GMP-induced currents increased in amplitude but did not reverse sign, for voltages 35-45 mV more positive than the dark, resting voltage. We conclude that light causes the simultaneous change in concentration of an intracellular messenger for excitation in addition to cyclic GMP, or that a change in the cytosolic concentration of cyclic GMP is not a step in the excitatory process.

Ambystoma↗
PubMed1984

Observations on rod coupling in the isolated retina of Bufo marinus.

Rod coupling was studied in the superfused isolated retina of Bufo marinus. Pairs of interacting rods were simultaneously impaled; current injected into one rod caused a current-induced potential in the second rod. Current-induced potentials and input resistance were monitored while changing the superfusate. Interactions were not reduced by removing extracellular Na+ or Cl-, indicating that these conductances do not mediate coupling. Interactions were not eliminated by altering extracellular Ca2+ or decreasing intracellular pH; the interactions are thus resistant to treatments that uncouple cels in other systems.

Animals↗
PubMed1984

Visually evoked eye movements in mouse mutants and inbred strains. A screening report.

The authors screened various inbred strains and mutants of the mouse, Mus musculus, for qualitatively abnormal or reduced numbers of optokinetic nystagmus (OKN) eye movements. Thirteen hypopigmentation mutants and ten neuromuscular mutants were found to have abnormal or markedly reduced OKN, but none of these mutants had retinal degeneration. Ten other hypopigmentation mutants and nine other neuromuscular mutants had relatively normal OKN, thus showing that neither hypopigmentation nor neuromuscular abnormality per se are well-correlated with abnormal OKN. These findings show that many mutants with visual defects are available from existing holdings. These visual mutants may serve as a resource for the study of the function and development of the mammalian visual system.

Animals↗
PubMed1983

Discrete visual defects in pearl mutant mice.

The mutant mouse pearl, characterized by its hypopigmentation, has a specific functional defect in a sensory system--the retina. The intact pearl mouse has reduced sensitivity in the dark-adapted condition. Normal sensitivity is restored by isolation and superfusion of the retina with bicarbonate-buffered Ringer solution, suggesting that the retinal expression of the pearl mutation depends on a diffusible substance. The pearl phenotype is described as a possible model for human congenital stationary night blindness.

Animals↗
PubMed1983

Modulation of membrane conductance in rods of Bufo marinus by intracellular calcium ion.

Double-barrel micropipettes were used to pressure-inject EGTA into the outer segments of rods in the isolated retina of Bufo marinus. We used these pipettes to point voltage clamp the cell to its resting membrane voltage during the injection of EGTA in order to prevent changes in membrane voltage from occurring. The input conductance of the rod was assessed by measuring the incremental membrane current required to hyperpolarize the membrane by less than or equal to 10 mV. When the retina was bathed in normal Ringer solution, the injection of EGTA during point voltage clamp evoked an inward membrane current and in increase in input conductance. This observation is consistent with an EGTA-evoked increase in conductance for an ion with an equilibrium potential more depolarized than the resting membrane potential. Injections of control solutions that did not contain EGTA had no effect. The effects of injected EGTA were not altered by variations in the pH or buffering capacity of the injection solution, or by the addition of equimolar Mg2+. Furthermore, injections of a solution containing equimolar Ca2+ and EGTA were without effect. Thus, the observed effects of injected EGTA were due to the lowering of the [Ca2+]i. Replacement of extracellular Na+ with choline+ abolished both the response to light and the EGTA-evoked increase in input conductance. A low [Na+]o solution containing 10(-8) M-Ca2+ reduced the response to injected EGTA by approximately the same amount as it reduced the response to light. Replacement of extracellular Cl- by methanesulphonate was without significant effect on either the response to light or to injected EGTA. These results are consistent with the interpretation that a lowered [Ca2+]i increases primarily the sodium conductance, gNa, of the plasma membrane of the rod outer segment. The conductance that is affected by a lowered [Ca2+]i appears to have the same specificity as the light-dependent conductance. This conclusion is consistent with a hypothesis for visual transduction involving modulation of gNa by light-evoked changes in the [Ca2+]i.

Animals↗
PubMed1982

Electrophysiology of retinal ganglion cells in the mouse: a study of a normally pigmented mouse and a congenic hypopigmentation mutant, pearl.

1. The organization of the receptive fields of retinal ganglion cells in te normal mouse was studied qualitatively in recordings from 43 single axons in the optic nerve and optic tract, and the light sensitivity was studied quantitatively in 26 of these cells by measuring incremental sensitivity. 2. The receptive fields of normal animals were elliptical, had concentric center and peripheral subdivisions, and had an antagonistic center/surround organization; the receptive-field centers ranged from 1.95 to 83 degrees in diameter, with a median of 7 degrees. 3. The incremental sensitivity to white light was measured using a criterion response of 10 extra spikes; the most sensitive dark-adapted cell required a stimulus luminance of 3.5 x 10(-3) cd/m2 to generate a criterion response. 4. The action spectrum measured at seven different wavelengths (433-619 nm) from ganglion cells in the normally pigmented mouse resembled the CIE (International Commission on Illumination, CIE 1957 (11)) relative scotopic luminous efficiency function (41) and is consistent with a curve having a peak around 500 nm. 5. On light adaptation with blue light (less than 460 nm), the sensitivity to longer wavelength stimuli increased by 0.2-0.5 log units relative to the sensitivity to the shorter wavelengths; these results are compatible with the presence of a photoreceptor sensitive to long wavelengths in the normally pigmented mouse (C57BL/6J+/+). 6. The organization of the receptive fields of 48 retinal ganglion cells from the hypopigmentation mutant pearl (C57BL/6J-pe) was also studied qualitatively; the receptive field organization was similar to that of the normally pigmented mouse. 7. In 25 cells from dark-adapted pearl mice, the incremental sensitivity to white light was, on the average, 1.6 log units less than that for normal mice. 8. The dark-adapted action spectrum of pearl mice was similar to that of normally pigmented mice. However, a shift in sensitivity to longer wavelengths did not occur on selective light adaptation with the most luminous blue light (less than 460 nm) background that we could produce. 9. We conclude that pearl is one of the mammalian genes that codes for functions that affect dark-adapted retinal sensitivity. The results of this study and past studies suggest that the pearl gene's action on light sensitivity is predominantly within the retina and before (distal to) the ganglion cells.

Adaptation, Physiological↗
PubMed1981

Interactions among rods in the isolated retina of Bufo marinus.

1. The existence and extent of interactions among rods were analysed in the isolated retina of Bufo marinus. Intracellular recordings were made from the outer segments with micropipettes. Stimuli of precisely measured geometry were delivered to the outer segments using a compound microscope. 2. To demonstrate the existence of interactions two rods were simultaneously impaled; current injected into one rod resulted in a current-induced potential of like sign in the other rod. 3. When the diameter of a circular stimulus was increased from 30 to 500 micrometer the mean sensitivity of the rods increased by 1.2 +/- 0.3 log units (S.D.), though the illuminance measured through the impaled rod was adjusted to be constant. 4. The extent of interactions was examined by presenting a dim, slit-shaped stimulus at each of several displacements from an impaled rod. This stimulus either passed through the retina before coming into focus on the outer segments (transillumination) or was focused directly on the outer segments (incident illumination). For each displacement both the amount of light scattered onto the impaled rod and the response of the rod were measured. 5. The amount of light scattered onto the impaled rod was assessed for each displacement of the stimulus. For incident illumination this assessment was made by measuring the distribution of bleached pigment about the slit stimulus. The bleaching could be described by an exponential that decreased with distance; this exponential had a space constant of 4 micrometer. For transillumination the assessment was made in two ways. The light that passed through the impaled rod was measured and found to decrease exponentially with slit displacement; the mean space constant of this exponentially was 9.3 +/- 3.2 micrometer (S.D.). In few experiments the distribution of bleached pigment about the slit stimulus was measured and was found to decrease exponentially with distance; this latter exponential had a slightly longer space constant than the exponential measured using transmitted light. 6. For each impaled rod a convolution of an exponential interaction function with the measured distribution of stimulus illuminance about the impaled rod could be fitted to the plot of response amplitude versus displacement of the slit stimulus. For stimuli presented by transillumination the mean space constant describing the interaction functions was 20 +/- 6 micrometer (S.D.). For stimuli presented by incident illumination the mean space constant of the interaction functions was 22 +/- 4 micrometer (S.D.). 7. This report presents new evidence that interactions among rods exist in the isolated retina and that the extent of interactions can be described by a space constant of about 20 micrometer.

Animals↗
PubMed1981

The interphotoreceptor matrix in rats with inherited retinal dystrophy.

The retinas of Royal College of Surgeons (RCS) rats with inherited retinal dystrophy and of genetic control RCS-rdy+ rats have been examined histochemically to determine whether the stainable interphotoreceptor matrix (IPM) is abnormal in dystrophic retinas. The mucosubstances that are stained with Alcian blue, Metachromatically stained with toluidine blue, or reacted with colloidal iron appear in normal retinas beginning on postnatal day 12 as an intense band of stain at the apical surface of the pigment epithelium and with less intense staining between the outer segments throughout the rest of the outer segment zone. In RCS retinas the distribution of stainable IPM differs from that in normal retinas beginning on day 12. At this time, there is a failure of the intense band of IPM staining to form completely at the apical surface of the pigment epithelium. As whorls of outer segment membranes accumulate due to the phagocytosis defect in RCS pigment epithelial cells, IPM staining almost disappears along the pigment epithelial cell surface and in the debris zone. In addition, the basal outer segment region stains much more heavily in RCS retinas than in normal retinas, a feature that presumably represents an abnormal accumulation of IPM in this region of mutant retinas. Since the abnormal distribution of stainable IPM is evident 6 to 8 days before the first pyknotic photoreceptor cell nuclei are seen, it may play a role in photoreceptor cell death in the RCS rat. Furthermore, since the difference in IPM distribution between mutant and normal retinas is first evident on the same day that disc shedding and phagocytosis begin in the normally developing retina, the abnormal IPM distribution in RCS rats may also be related to the phagocytosis defect in the mutant pigment epithelial cells.

Animals↗
PubMed1981

Characterization of abnormalities in the visual system of the mutant mouse pearl.

Mice of the mutant strain pearl (pe/pe) differ from the wild strain by a single gene mutation, which leads to a lightening of the coat color. We tested this strain to see if this mutant gene also expressed itself in one or more visual abnormalities. Pearl mice were found to lack totally the optokinetic nystagmus reflex that was present in every normal mouse that we examined. This lack of optokinetic nystagmus was not due to oculomotor defects, since postrotatory nystagmus was normal. As described for other pigmentation mutants, we found that pearl mutants had a reduced ipsilateral projection to the lateral geniculate nucleus, superior colliculus, and visual cortex. We recorded from single cells in the superior colliculus and found response properties and light sensitivities to be normal over the luminance range at which optokinetic nystagmus was tested. However, at very dim backgrounds (scotopic levels), the incremental sensitivities of these cells in pearl mice were about 100 times lower than those of normal mice. This reduction in sensitivity was restricted to scotopic backgrounds and was not due to abnormalities in either the time course of dark adaptation or the receptive field sizes of single cells. In recordings of the electroretinographic response, both the waveforms and the normalized magnitudes of the A and B waves of pearl were indistinguishable from those of normal mice, which seems to indicate that the cause of pearl's sensitivity defect is located central to the main electrical events in the photoreceptors. The normality of many aspects of the visual system of pearl mice contrasts sharply with the complete absence of optokinetic nystagmus, with the reduced ipsilateral projection, and with the reduced dark sensitivity of the cells in the superior colliculus.

Animals↗
PubMed1980

Progesterone induces a rapid increase in [Ca2+]in of Xenopus laevis oocytes.

Progesterone causes a rapid increase in the intracellular free calcium level in fully grown amphibian oocytes. When albino Xenopus laevis oocytes were microinjected with the Ca-specific photoprotein aequorin, the calcium-induced luminescence from this protein increased at 40-60 sec after the addition of progesterone and returned to the control level within 5-6 min. No further change in the aequorin glow could be detected through the remainder of the maturation period. This transient increase in cytoplasmic free calcium may be involved in controlling the resumption of oocyte maturation.

Aequorin↗
PubMed1978

Rapid light-induced changes in near infrared transmission of rods in Bufo marinus.

Rapid transient changes in axial transmission of near infrared light through the outer segments of retinal rods of Bufo marinus are induced by illumination. The reasons for these changes are not clear. The changes in optical transmission may be useful in the study of photoreceptor function. However, the study of photoreceptor functions through the use of indicator dyes may be confounded by the intrinsic light-induced changes of optical properties of the photoreceptor cells.

Animals↗
PubMed1978

Ionizable groups and conductances of the rod photoreceptor membrane.

The ionizable groups and conductances of the rod plasma membrane were studied by measuring membrane potential and input impedance with micropipettes that were placed in the rod outer segments. Reduction of the pH from 8.0 to 6.8 or from 7.8 to 7.3 resulted in membrane depolarization in the dark from 8.0 to 6.8 or from 7.8 to 7.3 resulted in membrane depolarization in the dark (by 2- 3 mV) and an increased size of the light response (also by 2-3 mV). The dark depolarization was accompanied by and increased resting input impedance (by 11-35 Momega). When the pH was decreased in a perfusate in which Cl(-) was replaced by isethionate, the membrane depolarized. When the pH was decreased in a perfusate in which Na(+) was replaced by choline, an increase of input impedance was observed (11-50 Momega) even though a depolarization did not occur. These results are consistent with the interpretation that the effects of decreased extracellular pH result mainly from a decrease in rod membrane K(+) conductance that is presumably cause by protonation of ionizable groups having a pK(a) between 7.3 and 7.8. Furthermore, from these results and results obtained by using CO(2) and NH(3) to affect specifically the internal pH of the cell, it seems unlikely that altered cytoplasmic [H(+)] is a cytoplasmic messenger for excitation of the rod. When the rods were exposed to perfusate in which Na(+) was replaced by choline, the resting (dark) input impedance increased (by 26 Momega +/- 5 Momega SE), and the light-induced changes in input impedance became undetectable. Replacement of Cl(-) by isethionate had no detectable effect on either the resting input impedance or the light-induced changes in input impedance. These results confirm previous findings that the primary effect of light is to decrease the membrane conductance to Na(+) and show that, if any other changes in conductance occur, they depend upon the change in Na(+) conductance. The results are consistent with the following relative resting conductances of the rod membrane: G(Na(+)) similar to G(K(+)) more than 2-5 G(Cl(-)).

Ambystoma↗
PubMed1977

Detection of light-induced changes of intracellular ionized calcium concentration in Limulus ventral photoreceptors using arsenazo III.

1. The metallochromic indicator dye, arsenazo III, was injected intracellularly into Limulus ventral photoreceptor cells to concentrations greater than 1 mM.2. The absorption spectrum (450-750 nm) of the dye in single dark-adapted cells was measured by a scanning microspectrophotometer. When a cell was light-adapted, the absorption of the dye changed; the difference spectrum had two maxima at about 610 and 660 nm, a broad minimum at about 540 nm and an isosbestic point at about 585 nm.3. When intracellular calcium concentration was raised in dark-adapted cells previously injected with arsenazo III, the difference spectum had two maxima at about 610 and 660 nm, a broad minimum at about 530 nm and an isosbestic point at about 585 nm. The injection of Mg(2+) into dark-adapted cells previously injected with the dye induced a difference spectrum that had a single maximum at about 620 nm. Also, decreasing the intracellular pH of cells previously injected with the dye induced a difference spectrum that had a minimum at about 620 nm. The evidence suggests that there is a rise of intracellular ionized calcium when a Limulus ventral photoreceptor is light-adapted.4. The intracellular calcium concentration, [Ca(2+)](1), in light-adapted photoreceptors was estimated to reach at least 10(-4)M by compaing the light-induced difference spectra measured in ventral photoreceptors with a standard curve determined in microcuvettes containing 2mM arsenazo III in 400 mM-KCl, 1 mM-MgCl(2) and 25 mM MOPS at pH 7.0.5. In cells injected to less than 3 mM arsenazo III, light induced a transient decrease in optical transmission at 660 nm (T(660)). This decrease in T(660) indicates that illumination of a ventral photoreceptor normally causes a transient increase of [Ca(2+)](1).6. Arsenazo III was found to be sensitive, selective and rapid enough to measure light-induced changes of intracellular ionized calcium in Limulus ventral photoreceptor cells.

Animals↗
PubMed1977

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

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.

Animals↗
PubMed1974

Light-induced changes in photoreceptor membrane resistance and potential in Gecko retinas. I. Preparations treated to reduce lateral interactions.

The time-course of the light-induced changes in membrane voltage and resistance were measured for single photoreceptors in the retina of Gekko gekko. In the surgically isolated retina, small stimuli directed toward the impaled receptor produced a membrane hyperpolarization the time-course of which was identical to that of the increase in membrane resistance. In the eyecup preparation nearly identical time-courses were evoked only after perfusion of the vitreous surface with solution having high (Mg(++)). Disparate time-courses were obtained in (a) the isolated retina when large or displaced stimuli were used, and (b) the eyecup preparation when it was treated normally (see Pinto and Pak. 1974. J. Gen. Physiol. 64:49) and when it was exposed to aspartate ions or hypoxia. These results are consistent with the hypothesis that the receptor potential (elicited in the impaled receptor as a result of quanta only it captures) is generated by a single ionic process that decreases membrane conductance. These measurements provide a means to distinguish the receptor potential from interactions. From direct measurements of membrane time constant and total resistance in darkness, total membrane capacitance was calculated. The mean capacitance was 7.1 x 10(-5) microF. This high value is consistent with anatomical observations of membrane infoldings at the base of gecko photoreceptors.

Animals↗