scholarly journals Light-Induced Changes in Photoreceptor Membrane Resistance and Potential in Gecko Retinas

1974 ◽  
Vol 64 (1) ◽  
pp. 26-48 ◽  
Author(s):  
L. H. Pinto ◽  
W. L. Pak
Keyword(s):  
Time Course ◽  
Membrane Conductance ◽  
Receptor Potential ◽  
Membrane Resistance ◽  
Photoreceptor Membrane ◽  
Membrane Hyperpolarization ◽  
Direct Measurements ◽  
Isolated Retina ◽  
Time Courses ◽  
Induced Changes

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 µF. This high value is consistent with anatomical observations of membrane infoldings at the base of gecko photoreceptors.

scholarly journals Light-Induced Changes in Photoreceptor Membrane Resistance and Potential in Gecko Retinas

1974 ◽  
Vol 64 (1) ◽  
pp. 49-69 ◽  
Author(s):  
L. H. Pinto ◽  
W. L. Pak
Keyword(s):  
Time Course ◽  
Receptor Potential ◽  
Membrane Resistance ◽  
Rapid Onset ◽  
Membrane Voltage ◽  
Peripheral Stimulus ◽  
Slow Increase ◽  
Membrane Hyperpolarization ◽  
Resistance Decrease ◽  
Induced Changes

The time-course of light-induced changes in membrane voltage and resistance were measured in single photoreceptors in eyecup preparations of Gekko gekko. A small circular stimulus directed toward the impaled receptor produced membrane hyperpolarization. Application of a steady annular light to the receptor periphery resulted in diminution of the receptor's response to the stimulus. The effects of illumination of the surrounding receptors were isolated by directing a small, steady desensitizing light to the impaled receptor and then applying a peripheral stimulus. Brief stimuli produced a transient decrease in resistance with rapid onset and offset, a time-course similar to that of the response diminution. For some cells a depolarization that coincided with the resistance decrease was seen. During illumination with prolonged stimuli the resistance decrease was followed by a slow increase. After offset resistance rose transiently above the original value and then returned slowly to its original value. The slow resistance changes were not accompanied by changes in membrane voltage. The response diminution, resistance decrease, and depolarization were not observed in retinas treated with aspartate or hypoxia. It is therefore concluded that these effects are mediated by horizontal cells. The diminution is achieved by shunting the receptor potential and may play a role in field adaptation.

K+-channel blockers do not decrease acetylcholine depolarizations in canine trachealis

1992 ◽  
Vol 70 (1) ◽  
pp. 43-52 ◽  
Author(s):  
E. E. Daniel ◽  
J. Jury ◽  
R. Serio ◽  
L. P. Jager
Keyword(s):  
Chloride Channels ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
Resting Potential ◽  
K Channel ◽  
Channel Blockers ◽  
Membrane Effects ◽  
Sucrose Gap ◽  
Time Courses

Using the double sucrose gap, we have examined the role of K+ channels in the cholinergic depolarizations in response to field stimulation and acetylcholine (Ach) in canine trachealis. Acetylcholine-like depolarization per se decreased electrotonic potentials from hyperpolarizing currents. The net effect of acetylcholine (10−6 M) depolarization on membrane conductance was a small increase after the depolarization was compensated by current clamp. Reversal potentials for acetylcholine depolarization and for the excitatory junction potential (EJP) were determined by extrapolation to be 20–30 mV positive to the resting potential, previously shown to be approximately −55 mV. They were shifted positively by tetraethylammonium ion (TEA) at 20 mM or Ba2+ at 1 mM. TEA or Ba2+ initially depolarized the membrane and increased membrane resistance. Repolarization of the membrane restored any reductions in EJP amplitudes associated with depolarization. After 15 min, the membrane potential partially repolarized, and acetylcholine-induced depolarization and contractions were then increased by TEA. 4-Aminopyridine depolarized the membrane but decreased membrane resistance. Apamin (10−6 M), charybdotoxin (10−7 M), and glybenclamide (10−5 M) each failed to significantly depolarize membranes, increase membrane resistance, or reduce EJP amplitudes or depolarization to 10−6 M Ach. Glybenclamide reduced depolarizations to added acetylcholine slightly. TEA occasionally reduced the EJP markedly, but this was shown to be most likely a prejunctional effect mediated by norepinephrine release. TEA alone among K+-channel blockers slowed the onset and the time courses of the EJP as well as the acetylcholine-induced depolarization. K+-channel closure cannot be a complete explanation of acetylcholine-induced membrane effects on this tissue. Acetylcholine must have increased the conductance of an ion with a reversal potential positive to the resting potential in addition to any effect to close K+ channels.Key words: acetylcholine, tracheal smooth muscle, trachea, chloride channels, sucrose gap, potassium channels, tetraethylammonium, Ba2+.

scholarly journals Properties of tetraethylammonium ion-resistant K+ channels in the photoreceptor membrane of the giant barnacle.

1981 ◽  
Vol 77 (6) ◽  
pp. 629-646 ◽  
Author(s):  
D R Edgington ◽  
A E Stuart
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Cardiac Glycosides ◽  
Time Course ◽  
Photoreceptor Membrane ◽  
K Channels ◽  
Na Pump ◽  
Tetraethylammonium Ion ◽  
Electrogenic Na Pump ◽  
Time Courses

After the offset of illumination, barnacle photoreceptors undergo a large hyperpolarization that lasts seconds or minutes. We studied the mechanisms that generate this afterpotential by recording afterpotentials intracellularly from the medial photoreceptors of the giant barnacle Balanus nubilus. The afterpotential has two components with different time-courses: (a) an earlier component due to an increase in conductance to K+ that is not blocked by extracellular tetraethylammonium ion (TEA+) or 3-aminopyridine (3-AP) and (b) a later component that is sensitive to cardiac glycosides and that requires extracellular K+, suggesting that it is due to an electrogenic Na+ pump. The K+ conductance component increases in amplitude with increasing CA++ concentration and is inhibited by extracellular Co++; the Co++ inhibition can be overcome by increasing the Ca++ concentration. Thus, the K+ conductance component is Ca++ dependent. An afterpotential similar to that evoked by a brief flash of light is generated by depolarization with current in the dark and by eliciting Ca++ action potentials in the presence of TEA+ in the soma, axon, or terminal regions of the photoreceptor. The action potential undershoot is generated by an increase in conductance to K+ that is resistant to TEA+ and 3-AP and inhibited by Co++. The similarity in time-course and pharmacology of the hyperpolarization afterpotentials elicited by (a) a brief flash of light, (b) depolarization with current, and (c) an action potential indicates that Ca++-dependent K+ channels throughout the photoreceptor membrane are responsible for all three hyperpolarizing events.

Excitation–contraction coupling in crab muscle fibers with swollen T tubules

1985 ◽  
Vol 63 (7) ◽  
pp. 879-885 ◽  
Author(s):  
J. H. Leal-Cardoso ◽  
G. Suarez-Kurtz
Keyword(s):  
Time Course ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Membrane Excitability ◽  
High Potassium ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Voltage Dependent ◽  
T Tubules

Single crab (Callinectes danae) fibers were equilibrated with isotonic, high KC1 solutions and were subsequently returned to the control saline. This caused marked swelling of the T tubules. Fibers treated with 100 mM KCl had a 2.5-mV residual depolarization, a 50% decrease in effective membrane resistance (Reff) and a 75% reduction in membrane time constant (τm). These fibers exhibited large increases in membrane conductance upon depolarization and were inexcitable; membrane depolarization with current pulses elicited no contraction. The effects of the KCl treatment on membrane properties were not reproduced by treatment with high potassium gluconate solutions, which did not cause tubular swelling. Tetrabutylammonium (10 mM) or Ba ions (10–20 mM), but not tetraethylammonium (40–100 mM), Sr ions (15–70 mM), or procaine (1–8 mM) reversed the effects of the KCl treatment on Reff, τm, membrane excitability, and excitation–contraction coupling. The time course of the Ba effects was consistent with the suggestion that the KCl treatment increases the K conductance of the tubular membranes, which in turn prevents the activation of voltage-dependent Ca channels located in the membranes of the T system. This results in inhibition of the Ca-dependent electrogenesis and consequently, the absence of contraction upon depolarization of the plasma membrane.

scholarly journals Adaptation in the Ventral Eye of Limulus is Functionally Independent of the Photochemical Cycle, Membrane Potential, and Membrane Resistance

1973 ◽  
Vol 61 (3) ◽  
pp. 273-289 ◽  
Author(s):  
A. Fein ◽  
R. D. DeVoe
Keyword(s):  
Membrane Potential ◽  
Time Constant ◽  
Dark Adaptation ◽  
Light Adaptation ◽  
Receptor Potential ◽  
Membrane Resistance ◽  
Initial Time ◽  
Early Receptor Potential ◽  
Time Courses ◽  
Sensitivity Changes

The early receptor potential (ERP), membrane potential, membrane resistance, and sensitivity were measured during light and/or dark adaptation in the ventral eye of Limulus. After a bright flash, the ERP amplitude recovered with a time constant of 100 ms, whereas the sensitivity recovered with an initial time constant of 20 s. When a strong adapting light was turned off, the recovery of membrane potential and of membrane resistance had time-courses similar to each other, and both recovered more rapidly than the sensitivity. The receptor depolarization was compared during dark adaptation after strong illumination and during light adaptation with weaker illumination; at equal sensitivities the cell was more depolarized during light adaptation than during dark adaptation. Finally, the waveforms of responses to flashes were compared during dark adaptation after strong illumination and during light adaptation with weaker illumination. At equal sensitivities (equal amplitude responses for identical flashes), the responses during light adaptation had faster time-courses than the responses during dark adaptation. Thus neither the photochemical cycle nor the membrane potential nor the membrane resistance is related to sensitivity changes during dark adaptation in the photoreceptors of the ventral eye. By elimination, these results imply that there are (unknown) intermediate process(es) responsible for adaptation interposed between the photochemical cycle and the electrical properties of the photoreceptor.

Alpha 1-adrenergic receptor activation depolarizes rat supraoptic neurosecretory neurons in vitro

1986 ◽  
Vol 251 (3) ◽  
pp. R569-R574 ◽  
Author(s):  
J. C. Randle ◽  
C. W. Bourque ◽  
L. P. Renaud
Keyword(s):  
Time Course ◽  
Membrane Resistance ◽  
Receptor Activation ◽  
Membrane Hyperpolarization ◽  
Neurosecretory Neurons ◽  
Consistent Change ◽  
K Current ◽  
Supraoptic Neurons ◽  
A Current

Intracellular data were obtained from 35 supraoptic nucleus neurosecretory neurons maintained in vitro in intra-arterially perfused explants of rat hypothalamus. Addition of norepinephrine, phenylephrine, or methoxamine, but not isoproterenol (30-200 microM), consistently induced membrane depolarization, bursting activity, and an associated prolongation in action potential duration, effects that were reversibly antagonized by the alpha 1-antagonist prazosin. Norepinephrine-evoked depolarizations demonstrated no consistent change in membrane resistance and were reduced both by membrane hyperpolarization and by raising extracellular K+. Norepinephrine shortened the time course of spike hyperpolarizing afterpotentials and increased the magnitude of late depolarizing afterpotentials. It is proposed that one of norepinephrine's actions on supraoptic neurons involves K+ channels, perhaps by modulation of a transient K+ current known as A current.

Two Types of Identified Ascending Interneurons With Distinct GABA Receptors in the Crayfish Terminal Abdominal Ganglion

1997 ◽  
Vol 77 (3) ◽  
pp. 1213-1223 ◽  
Author(s):  
Hiroki Miyata ◽  
Toshiki Nagayama ◽  
Masakazu Takahata
Keyword(s):  
Lateral Inhibition ◽  
Gaba Receptors ◽  
Time Course ◽  
Reversal Potential ◽  
Membrane Conductance ◽  
Sensory Stimulation ◽  
Abdominal Ganglion ◽  
Membrane Hyperpolarization ◽  
Inhibitory Postsynaptic Potentials ◽  
Bath Application

Miyata, Hiroki, Toshiki Nagayama, and Masakazu Takahata. Two types of identified ascending interneurons with distinct GABA receptors in the crayfish terminal abdominal ganglion. J. Neurophysiol. 77: 1213–1223, 1997. More than half of the identified ascending interneurons originating in the terminal abdominal ganglion of the crayfish received inhibitory sensory inputs from hair afferents innervating the tailfan on the side contralateral to their main branches. Biochemical aspects of this transverse lateral inhibition of ascending interneurons were examined by the use of neurophysiological and pharmacological techniques. Local application of γ-aminobutyric acid (GABA) and its agonist muscimol into the neuropil induced membrane hyperpolarization of identified ascending interneurons with an increase in membrane conductance. Because the reversal potential of inhibitory postsynaptic potentials (IPSPs) in ascending interneurons elicited by the sensory stimulation and GABA injection was similar, and the sensory-stimulated IPSPs of the interneurons were blocked by GABA and muscimol application, this study strongly suggests a GABAergic nature for transverse lateral inhibition of ascending interneurons. According to the response to the GABAA antagonists bicuculline and picrotoxin, ascending interneurons were classified into two types, picrotoxin-sensitive and picrotoxin-insensitive interneurons. Identified ascending interneurons VE-1 and RO-4 showed a pharmacological profile similar to that of the classical GABAA receptor of the vertebrates. Bath application of both bicuculline and picrotoxin reversibly reduced the amplitudes of IPSPs. The other identified ascending interneurons CA-1, RO-1, and RO-2 were not affected significantly by the bath application of GABAA and GABAB antagonists, although bath application of low-chloride saline reversed the sensory-stimulated IPSPs. IPSPs of the picrotoxin-sensitive interneurons had a rather faster time course and shorter duration in comparison with those of the picrotoxin-insensitive interneurons.

scholarly journals Hyperpolarization of a Barnacle Photoreceptor Membrane following Illumination

1971 ◽  
Vol 57 (6) ◽  
pp. 723-737 ◽  
Author(s):  
H. Koike ◽  
H. Mack Brown ◽  
S. Hagiwara
Keyword(s):  
Membrane Potential ◽  
Time Course ◽  
Membrane Conductance ◽  
Resting Potential ◽  
Photoreceptor Membrane ◽  
Electrogenic Na Pump ◽  
Lateral Ocellus ◽  
Na Ions ◽  
Conductance Increase ◽  
Balanus Eburneus

Membrane potential changes following illumination of a photoreceptor cell in the lateral ocellus of a barnacle (Balanus eburneus) were studied by means of intracellular recording and polarization techniques. Illumination produces a depolarizing response. When the illumination is terminated, the membrane potential temporarily becomes more negative than the resting potential prior to illumination. Although the amplitude of this postillumination hyperpolarization depends upon the intensity as well as the duration of the light pulse, the time course is fairly constant. The hyperpolarization is not associated with any significant membrane conductance increase and is abolished by 10-5 M ouabain. It diminishes when the external Na or K ions are removed. An intracellular injection of Na ions produces a hyperpolarization similar to that following illumination. It is suggested that the postillumination hyperpolarization is produced by an electrogenic Na pump which is activated by the Na influx during illumination.

scholarly journals Early Receptor Potentials of Rods and Cones in Rodents

1966 ◽  
Vol 49 (6) ◽  
pp. 1199-1208 ◽  
Author(s):  
WILLIAM L. PAK ◽  
THOMAS G. EBREY
Keyword(s):  
Time Course ◽  
Light Adaptation ◽  
Receptor Potential ◽  
Ground Squirrels ◽  
Wave Form ◽  
Second Phase ◽  
Response Curves ◽  
Early Receptor Potential ◽  
Time Courses ◽  
Cone Potential

The second phase (negative peak) of the early receptor potential of cones has been studied in the all-cone eyes of the Mexican and antelope ground squirrels (Citellus mexicanus and Citellus leucurus) and compared with responses from the rod-dominant eyes of the rat and flying squirrel (Glaucomys volans). The responses obtained from the all-cone eyes tended to be smaller in amplitude, to have higher thresholds, and to be considerably more resistant to light adaptation than the responses from the rod-dominant eyes. The wave forms and time courses of the two types of responses were similar, although the cone potential tended to be less sensitive to temperature variations and its time constants tended to be shorter than those of the rod potential. The spectral sensitivity of the second phase of the early receptor potential of the Mexican ground squirrel closely follows the absorption spectrum of a Dartnall nomogram pigment having its absorption maximum at 540 mμ. Moreover, as in the case of the rat, the amplitude of the response appears to be linearly related to the amount of pigment bleached in a flash. Thus, in both all-rod and all-cone systems the early receptor potential appears to arise in the photoexcitation of the respective visual pigment and appears to be closely linked to the initial photochemical events. The similarity of the wave form, time course, and stimulus-response curves in the two systems suggests that the early receptor potential is produced by similar mechanisms in all-rod and all-cone systems.

Inactive Renin in Rabbit Plasma: Effect of Frusemide

1981 ◽  
Vol 60 (4) ◽  
pp. 393-398 ◽  
Author(s):  
H. K. Richards ◽  
D. J. Lush ◽  
A. R. Noble ◽  
K. A. Munday
Keyword(s):  
Plasma Levels ◽  
Time Course ◽  
Rabbit Plasma ◽  
Active Renin ◽  
Inactive Form ◽  
Plasma Active Renin ◽  
Inactive Renin ◽  
Time Courses ◽  
Induced Changes ◽  
Sodium And Potassium

1. An inactive form of renin exists in rabbit plasma. This can be activated, and therefore measured, after acidification (pH 2.8). 2. The effect of frusemide diuresis, with replacement of volume losses, on plasma levels of active and inactive renin was studied over a 3 1/2 h time course. Plasma active renin increased during frusemide diuresis but inactive renin disappeared from the circulation. The time courses for the changes in the two forms of renin were similar. 3. The peak of the frusemide-induced changes in renal function (urine flow, sodium and potassium excretion and creatinine clearance) preceded the maximum changes in the two forms of renin by 90 min. 4. The response of plasma levels of inactive renin to physiological stimuli depends on the nature of the stimulus, as well as its duration. Some form of sodium-sensitive mechanism may control the activation of inactive renin.

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