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Biomedical subjects

E A Schwartz

Publications and source records attributed to E A Schwartz.

At least 19 recordsLinked to original sources
PubMed1995

Optical analyses of eyeglass lens fragments and the unexpected detection of oral sperm in a homicide case.

A homicide case in which intact spermatozoa were found in the oral cavity of the deceased forty days after his disappearance is reported. The victim's partially frozen body was found outdoors in a wooded area of upstate New York during the month of January. During a subsequent investigation, pieces of eyeglass lens fragments and bloodstains were found in the suspect's house and vehicle. Chemical and optical analyses of the lens fragments are presented as well as results of the serological tests.

Adult↗
PubMed1994

A cGMP-gated current can control exocytosis at cone synapses.

The voltage-gated Ca2+ current in cone photoreceptors operates over only a small part of the physiological voltage range produced by light and, consequently, appears insufficient for controlling transmitter release. We have used a whole-cell voltage clamp to measure membrane current and the capacitance change produced by exocytosis in solitary cone and rod photoreceptors isolated from the salamander retina. In both types of photoreceptor, Ca2+ influx through voltage-gated Ca2+ channels initiated exocytosis. In addition, Ca2+ influx through a cGMP-gated channel in the inner segment and synaptic processes of cones also initiated exocytosis. The cGMP-gated current sustained exocytosis over the entire physiological voltage range.

Ambystoma↗
PubMed1994

A GABA transporter operates asymmetrically and with variable stoichiometry.

Membrane currents produced by the expression of a rat GABA transporter (GAT-1) stably transfected into HEK293 cells were characterized with a whole-cell voltage clamp. Three modes of function were identified: ex-gated currents produced by extracellular GABA, in-gated currents produced by intracellular GABA, and uncoupled currents produced in the absence of GABA. The ex-gated current was not the reversal of the in-gated current; moreover, the stoichiometry between GABA and co-ions was not always fixed. Each mode of function required a different set of ions on the two sides of the membrane. We made rapid solution changes and observed an allosteric effect of Na+ that only occurred at the extracellular surface. Thus, the GAT-1 transporter does not behave like a recirculating carrier but may be described as a pore with ion gates at either end that are controlled in part by allosteric sites.

Allosteric Site↗
PubMed1993

L-glutamate conditionally modulates the K+ current of Müller glial cells.

L-Glutamate inhibits the K+ conductance that dominates the electrical behavior of a Müller glial cell. The effect of glutamate is enhanced by simultaneous exposure to dopamine. L-Glutamate acts at a metabotropic receptor that controls the K+ conductance through two pathways. A rapid pathway produces a partial inhibition in less than 2 s. Thereafter, a slow pathway progressively inhibits the conductance with a half-time of minutes. Pathways initiated by L-glutamate and dopamine appear to converge on and stimulate adenylyl cyclase. A subsequent step is the activation of a cAMP-dependent protein kinase, PKA. The local overflow of L-glutamate from active synapses may functionally remove K+ channels from nearby glial membranes. A uniform rise in extracellular L-glutamate concentration, as might occur during pathological conditions, should suppress a glial cell's K+ conductance and allow other voltage-dependent processes to be influenced by depolarization.

Adenylate Cyclase Toxin↗
PubMed1993

Ions required for the electrogenic transport of GABA by horizontal cells of the catfish retina.

1. Solitary horizontal cells were isolated from catfish retinas. Membrane currents activated by extracellular and intracellular GABA were characterized during a whole-cell voltage clamp. 2. Extracellular GABA activated two currents: a GABAA current, and an 'influx' current mediated by a GABA transporter. The influx current was studied after the GABAA current was blocked with 0.5 mM picrotoxin. The influx current required extracellular Na+ and Cl-. Extracellular Na+ could not be replaced by another alkali metal cation. 3. The influx current also depended upon the identity of ions in the intracellular solution. Either an intracellular alkali metal cation or Cl- was required to produce an influx current. 4. The influx current was inward at -75 mV and decreased as the membrane was depolarized towards +20 mV. When the membrane was depolarized beyond +25 mV, the polarity of the current depended upon the ion composition of the intracellular solution and could be inward, zero or outward. 5. The introduction of GABA into a cell during the course of an experiment produced an outward current. This 'efflux' current was small at -75 mV and increased with depolarization. The efflux current required intracellular Na+ and Cl-. Intracellular Na+ could not be replaced by another alkali metal cation. 6. The efflux current also depended upon the identity of ions in the extracellular solution. An extracellular alkali metal cation was required to produce an efflux current. Removing extracellular Cl- did not affect the efflux current. 7. The outward movement of GABA produced a local accumulation in extracellular GABA concentration that could be detected by the activation of the GABAA current. GABA efflux only occurred during conditions that produced an efflux current. Electroneutral efflux did not occur. 8. In the absence of GABA, extracellular alkali metal cations produced a 'leakage' current. The leakage current was inward at -75 mV and decreased as the membrane was depolarized towards +20 mV. When the membrane was depolarized beyond +25 mV, the polarity of the leakage current depended, like the GABA influx current, upon the ion composition of the intracellular solution and could be inward, zero or outward. The addition of GABA to the intracellular solution produced an efflux current and suppressed the leakage current. 9. We conclude that the transporter mediates electrogenic influx, efflux and leakage. Each mode of operation depends upon ions on both sides of the membrane. Influx and efflux are not symmetrical.

Animals↗
PubMed1992

Hemi-gap-junction channels in solitary horizontal cells of the catfish retina.

1. Solitary horizontal cells were isolated from catfish retinas and their membrane current was recorded with a whole-cell voltage clamp. Reducing the extracellular Ca2+ concentration produced a current that could be suppressed by dopamine. This Ca(2+)- and dopamine-sensitive current is hereafter termed I gamma. The voltage dependence, cytoplasmic regulation, and permeability of the I gamma channel suggest that it is half of a gap-junction channel. 2. I gamma was voltage and time dependent. In the steady state, the current-voltage relation displayed outward rectification at voltages more depolarized than 0 mV and a negative resistance region at voltages more hyperpolarized than -15 mV. The reversal potential was 3.3 +/- 1.5 mV when NaCl was the predominant extracellular salt and potassium-D-aspartate was the predominant intracellular salt. 3. The size of I gamma depended on the extracellular Ca2+ concentration. I gamma was maximal at external Ca2+ concentrations below 10 microM, half-maximal at 220 microM-Ca2+, and reduced to less than 4% of its maximum amplitude at external Ca2+ concentrations above 1 mM. Increasing the extracellular Ca2+ concentration reduced the amplitude of I gamma without changing the shape of the current-voltage relation or the kinetics of inactivation. Thus, rectification does not result from a voltage-dependent block by extracellular Ca2+. 4. Patches of cell membrane were voltage clamped in both the cell-attached and excised-patch configurations. In the cell-attached configuration, the addition of dopamine to the solution outside the patch pipette blocked the opening of channels within the membrane patch. Thus, dopamine closes I gamma channels by initiating an intracellular messenger cascade. In the excised-patch configuration, a maximum conductance of 145 pS was measured while Cs+ and tetraethylammonium+ (TEA+) were the only monovalent cations on both sides of the membrane. 5. The ability of dopamine to suppress I gamma was blocked by introducing an inhibitor of the cyclic AMP-dependent protein kinase, PKI5-24, into the cytoplasm. Thus, the action of dopamine is mediated by a pathway that includes the activation of a cyclic AMP-dependent kinase. 6. I gamma was suppressed by nitroprusside, an agent which activates guanylate cyclase and increases the intracellular cyclic GMP concentration. The effect of nitroprusside was not altered by the intracellular application of PKI5-24. Thus, nitroprusside suppresses I gamma through a pathway that does not include the activation of a cyclic AMP-dependent kinase.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Characterization of deoxyribonucleic acid (DNA) obtained from teeth subjected to various environmental conditions.

This study was designed to determine the effects of various environmental factors on the deoxyribonucleic acid (DNA) obtained from dental pulp. Extracted teeth were subjected to the following conditions: varying pH (3,7,10); temperature (4 degrees C, 25 degrees C, 37 degrees C, incineration); humidity (20%, 66%, 98%); various types of soil (sand, potting soil, garden soil); seawater; burying the teeth outdoors, and aging (one week to six months). In addition, teeth that had been extracted and held at room temperature for 16 and 19 years were also examined. Following isolation of DNA, the samples were analyzed on yield gels to determine the concentration and integrity of the recovered DNA. Restriction digestion with Pst I was followed by electrophoresis of the generated fragments, Southern transfer to nylon membranes, and hybridization to both human and bacterial probes. It was determined that, aside from soil, the environmental conditions examined did not affect the ability to obtain high-molecular-weight human DNA from dental pulp. Restriction fragment length polymorphic (RFLP) analysis of selected samples was performed. Dental pulp patterns were compared with bloodstain exemplars, revealing matching patterns, although an increase in band-shifting was observed with extended exposure to elevated temperatures.

Autoradiography↗
PubMed1990

Electrophysiology of glutamate and sodium co-transport in a glial cell of the salamander retina.

1. Müller cells were isolated from salamander retinas and their membrane voltage was controlled with a whole-cell voltage clamp. External D-aspartate, L-aspartate and L-glutamate each induced a membrane current. D-Glutamate, kainate, quisqualate and N-methyl-D-aspartate were more than 100x less effective than L-aspartate. Kynurenic acid had no effect on the current produced by L-glutamate, L-aspartate or D-aspartate. 2. The current induced by an acidic amino acid (AAA) was completely dependent on the presence of external Na+. Neither Li+, Cs+, choline nor TEA+ were able to substitute for Na+. The relationship between external Na+ concentration and current amplitude can be explained if the binding of three Na+ ions enabled transport. The apparent affinity constant for Na+ binding was 41 mM. Altering K+, H+ and Cl- concentrations demonstrated that these ions are not required for transport. 3. The shape of the current-voltage relation did not depend on the external amino acid concentration. The relationship between D-aspartate concentration and current amplitude can be described by the binding of D-aspartate to a single site with an apparent affinity constant of 20 microM. 4. Influx and efflux of AAA were not symmetric. Although influx was electrogenic, efflux did not produce a current. Moreover, influx stimulated efflux; but efflux inhibited influx. 5. Removing external Na+ demonstrated that Na+ carried a current in the absence of an AAA. Li+ was a very poor substitute for Na+. This current may be due to the uncoupled movement of Na+ through the transporter. The relationship between the external Na+ concentration and the amplitude of the uncoupled current can be explained if the binding of two or three Na+ ions enabled the translocation of Na+ in the absence of an AAA. The apparent affinity constant for Na+ binding was approximately 90 mM. 6. The temperature dependence of the AAA-induced current had a Q10 between 8 and 18 degrees C of 1.95. The Q10 is consistent with a rate constant for influx of 10(4) s-1 (at -70 mV and 20 degrees C). The maximum rate of influx was measured following a concentration jump produced by the photolysis of 'caged' L-glutamate. The onset of the observed current was limited by the 1.3 ms resolution of the recording system. Hence, the rate constant for influx must be faster than 10(3) s-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma↗
PubMed1989

Modulation of an electrical synapse between solitary pairs of catfish horizontal cells by dopamine and second messengers.

1. Retinas from channel catfish were dissociated and the cells maintained in culture. Horizontal cells that normally receive input from cone photoreceptors were identified. The conductance of the electrical junction formed between a pair of 'cone' horizontal cells was measured by controlling the membrane voltage of each cell with a voltage clamp maintained through either a micropipette or a patch pipette. The two techniques yielded similar results. 2. Transjunctional current was measured while transjunctional voltage was stepped to values between +/- 60 mV. The current (measured 5 ms after a step) was proportional to voltage over the range tested. For steps to voltages greater than +/- 45 mV, the current exhibited a slight time-dependent decline. 3. Dopamine decreased junctional conductance in a dose-dependent fashion. A 50% reduction was obtained with 10 nM-dopamine. The D1 agonist fenoldopam (100 nM) also decreased junctional conductance. The uncoupling produced by either agent was rapid and reversible. 4. The introduction of 100 microM-cyclic AMP into one cell of a pair decreased junctional conductance by, on average, 40%. Forskolin (1-10 microM), an activator of adenylate cyclase, decreased junctional conductance 50-90%. 5. The introduction of 80 microM-cyclic GMP into one cell of a pair decreased junctional conductance by, on average, 40%. Nitroprusside (1-10 microM), an activator of guanylate cyclase, reduced junctional conductance 40-65%. 6. The introduction of a peptide inhibitor specific for the cyclic AMP-dependent protein kinase reversed a decrease in junctional conductance produced by superfusion with either dopamine (1 microM), fenoldopam (100 nM) or forskolin (5-10 microM). 7. Intracellular Ca2+ concentration was measured with the fluorescent indicator Fura-2. The intracellular Ca2+ concentration was increased by activation of a Ca2+ current. Junctional conductance remained constant as the internal Ca2+ concentration changed from 100 to 700 nM. 8. Intracellular pH was measured with the fluorescent indicator bis-carboxyethylcarboxyfluorescein. The application of acetate (2.5 mM) reduced intracellular pH by 0.2-0.3 units and decreased junctional conductance by approximately 50%. A subsequent application of fenoldopam did not alter intracellular pH, but decreased junctional conductance by more than 50%. 9. The sensitivity of the junctional conductance between isolated horizontal cells to dopamine is consistent with dopamine having a direct effect on coupling in intact retina. Dopamine regulates the activity of a cyclic AMP-dependent protein kinase which in turn modulates junctional conductance. Changes in intracellular pH and Ca2+ concentration are not involved in mediating the effect of dopamine on coupling. Cyclic GMP and intracellular pH may participate in regulatory pathways independent of that used by cyclic AMP.

Animals↗
PubMed1987

Depolarization without calcium can release gamma-aminobutyric acid from a retinal neuron.

Calcium influx is often an essential intermediate step for the release of neurotransmitter. However, some retinal neurons appear to release transmitter by a mechanism that does not require calcium influx. It was uncertain whether depolarization released calcium from an intracellular store or released transmitter by a mechanism that does not require calcium. The possibility that voltage, and not calcium, can regulate the release of transmitter was studied with pairs of solitary retinal neurons. Horizontal and bipolar cells were isolated from fish retinas and juxtaposed in culture. Communication between them was studied with electrophysiological methods. A horizontal cell released its neurotransmitter, gamma-aminobutyric acid, when depolarized during conditions that buffered the internal calcium concentration and prohibited calcium entry. The speed and amount of material released were sufficient for a contribution to synaptic transmission.

Animals↗
PubMed1986

Synaptic transmission in amphibian retinae during conditions unfavourable for calcium entry into presynaptic terminals.

Toad (Bufo marinus) retinae were peeled from the pigment epithelium and superfused over the photoreceptor surface with a calcium-poor, cobalt-rich medium. The shape of the electroretinogram indicated that post-synaptic neurones received synaptic input. Adding the putative transmitters glutamate and N-acetylhistidine changed the shape of the electroretinogram. The change suggests that an excess of the putative transmitters blocked a component of synaptic transmission that persisted when a retina was bathed in cobalt. Salamander (Ambystomatigrinum) retinae in hemisected eye cups were superfused over their vitreal surface. Intracellular responses were recorded from photoreceptors. Reducing the calcium concentration in the superfusing medium from 1 mM to less than 10 microM slowly changed responses produced by light. The change indicates that the calcium concentration in the extracellular space surrounding photoreceptors fell to less than 100 microM. When retinae were superfused with a medium containing 1 mM-calcium, 3 mM-barium, and 10 mM-tetraethylammonium (TEA), rods produced action potentials that were later blocked by adding 1 mM-cobalt. Blocking calcium channels with cobalt and lowering the extracellular calcium concentration should together block calcium-dependent synaptic transmission. Intracellular responses were recorded from horizontal cells. After replacing external calcium with cobalt the membrane potential hyperpolarized and responses produced by light became smaller but did not entirely disappear. The responses that remained were less sensitive to light and had an altered shape. The change was reversible. Similar responses could be recorded after prolonged (30-120 min) exposure to cobalt. Electrical synapses between horizontal cells were uncoupled by adding 10 microM-forskolin to the cobalt medium. The polarity of a response could then be reversed if a cell was depolarized by injecting current. The observation of a reversal potential demonstrates that the response was produced by a conductance change. Intracellular responses were recorded from depolarizing and hyperpolarizing bipolar cells while retinae were superfused with cobalt-rich medium. After changing to a cobalt-free medium containing 1 mM-calcium, responses produced by light were slightly smaller. Large responses were recorded after superfusing with cobalt-rich, calcium-poor medium for 30-120 min. The results indicate that synaptic transmission by photoreceptors continues during conditions expected to block the entry of calcium into their presynaptic terminals.

Ambystoma↗
PubMed1984

Control of the generator current in solitary rods of the Ambystoma tigrinum retina.

THe current suppressed by light, the generator current, was studied in solitary salamander (Ambystoma tigrinum) rod photoreceptors with the single-micropipette voltage-clamp technique. The effects of Ca, cyclic GMP, and voltage were measured while voltage- and Ca-activated currents of the inner segment were blocked with Co, Cs, and TEA (tetraethylammonium). The generator current was increased more than 5-fold by lowering the external Ca concentration from 1.5 mM to 10 microM. The generator current could be decreased approximately 1/2 by injecting Ca into an outer segment. Injection of EGTA quickly increased the generator current approximately 2-fold. After injection ceased, the increase was quickly reversed. The generator current could be increased more than 5-fold by injecting cyclic GMP or 8Br-cyclic GMP. Injection of protons, the pH buffer bicine (N,N-bis[2-hydroxyethyl]glycine), or GMP did not produce a change in the generator current. The current-voltage curve for the generator current was influenced by external Co: in 3 mM-Co the current-voltage curve had a negative resistance between -45 and -90 mV; in 0.1 mM-Co the current-voltage curve paralleled the voltage axis between -45 and -90 mV. The difference is attributed to a voltage-dependent block by Co. Susceptibility to the blocking action of Co was reduced by lowering internal or external Ca concentration, or by injecting cyclic GMP. When rods were bathed in a medium containing 7-100 microM-Ca, a step depolarization produced a time-dependent decline in current. Because the reversal potential remained constant, the decline is attributed to an inactivation. The extent of inactivation was reduced by increasing the concentration of external Ca or injecting cyclic GMP.

Ambystoma↗
PubMed1984

The calcium current in inner segments of rods from the salamander (Ambystoma tigrinum) retina.

Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the 'whole-cell, gigaseal' technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). The soluble constituents of the cytoplasm exchanged with the solution in the pipette. The external solution could be changed during continuous perfusion. Membrane voltage was controlled with a voltage clamp. After permeant ions other than Ca were replaced with impermeant ions (i.e. tetraethylammonium as a cation, and aspartate or methanesulphonate as an anion), an inward current remained. It activated at approximately -40 mV, reached a maximum at approximately 0 mV, and decreased as the membrane was further depolarized. The size of the current increased when Ba was substituted for external Ca. The current was blocked when Ca was replaced with Co. The voltage at which the current was half-maximum shifted from approximately -22 to -31 mV during the initial 3 min of an experiment. The maximum amplitude of the current continuously declined during the entire course of an experiment. The time course for activation of the Ca current following a step of depolarization could be described by the sum of two exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of two exponentials. Both time constants for deactivation were independent of voltage (between -30 and 0 mV) and faster than the slower time constant for activation. When the internal Ca concentration was buffered by 10 mM-EGTA, the Ca current did not inactivate during several seconds of maintained depolarization. When the concentration of EGTA was reduced to 0.1 mM, the Ca current declined and the membrane conductance decreased during several seconds of maintained depolarization. This inactivation was incomplete and only occurred after a substantial quantity of Ca entered. Following repolarization the Ca conductance recovered from inactivation. In contrast, the continuous decline observed during the course of an experiment (item 3) was not reversible. The difference suggests that inactivation and the decline are distinct processes.

Ambystoma↗
PubMed1983

Evidence for the identification of synaptic transmitters released by photoreceptors of the toad retina.

1. When toad retinae were incubated with veratrine, kainic acid, and L-alpha-aminoadipic acid, photoreceptor cells survived and most other neurones died. This preparation of 'isolated' photoreceptor cells accumulated radioactive molecules from the incubation medium and metabolized these into labelled compounds. When a preparation was placed on a filter and superfused, radioactive molecules which were released into the superfusion fluid could be collected and later analysed. Several procedures were used for inducing the release of possible transmitter compounds. Each released compound was chemically identified. 2. Three compounds, aspartic acid, glutamic acid, and N-acetyl histidine, were released when the potassium concentration was increased in media that lacked calcium and contained cobalt. 3. The release of these compounds was further increased when cobalt was removed and calcium returned to the extracellular medium. 4. Two additional compounds, putrescine and cadavarine, were also released during depolarization when calcium was present. 5. The efflux of each of the compounds listed in Section 2 was also increased by homo- and hetero-exchange. For at least aspartate, exchange was sodium-dependent. 6. The post-synaptic effect of released compounds was tested by their ability to increase the efflux of [3H]GABA from 'isolated' horizontal cells. 0 . 1 mM-L-aspartate, or L-glutamate produced an increase in GABA efflux. N-acetyl histidine, putrescine, and cadavarine were ineffective. 7. Isolated photoreceptors and intact retinae were incubated with [3H]aspartate, or [3H]putrescine. Subsequent histology and autoradiography demonstrated that both compounds were selectively accumulated by cones.

Animals↗
PubMed1982

Calcium-independent release of GABA from isolated horizontal cells of the toad retina.

1. When toad retinae were incubated first with veratrine, then with antibodies that reacted with the outer segments of photoreceptors, and finally with complement, horizontal cells survived and most other neurones died. This preparation of 'isolated' horizontal cells accumulated radioactive GABA from the incubation medium. The subsequent release of radioactive GABA could then be measured. 2. The efflux of GABA was increased by exposure to an elevated potassium concentration or added glutamate. Both procedures are known to depolarize horizontal cells. 3. GABA in the external medium also increased the efflux of GABA. 4. The increase in GABA efflux produced by an elevated potassium concentration was unaffected with calcium in the external medium was replaced with cobalt and when sodium was replaced with choline or lithium. 5. The increase in GABA efflux produced by glutamate was unaffected when calcium was replaced with cobalt and when sodium was replaced with lithium, but was inhibited when sodium was replaced with choline. 6. The increase in GABA efflux produced by external GABA was unaffected when calcium was replaced with cobalt but required sodium. Neither choline nor lithium would substitute for sodium. 7. An increase in GABA efflux was accompanied by an increase in sodium efflux. 8. After a high concentration of GABA (2-20 mM) had produced a maximal increase in GABA efflux, the addition of glutamate produced no further effect. Conversely, after a high concentration of glutamate (2-20 mM) had produced a maximal increase in efflux, the addition of external GABA produced only a small further increase. These and the preceding results could occur if GABA release were mediated by a carrier system which could be activated by either depolarization or homoexchange.

Animals↗
PubMed1982

Voltage-activated and calcium-activated currents studied in solitary rod inner segments from the salamander retina.

1. Solitary rod inner segments were obtained by enzymatic dissociation of the tiger salamander (Ambystoma tigrinum) retina. Their membrane currents were studied with the single-pipette voltage-clamp technique. Individual currents were isolated with the aid of pharmacological agents.2. Extracellular caesium blocked a current activated by hyperpolarization from -30 mV. Changing external sodium and potassium concentrations altered the value of the reversal potential in a manner consistent with the current being carried equally by both ions.3. Extracellular tetraethylammonium (TEA) blocked a current activated by depolarization from -70 mV. In normal medium this current had a reversal potential of -72 mV. Changing the external potassium concentration altered the value of the reversal potential in a manner consistent with the current being carried predominantly by potassium.4. Extracellular cobalt blocked a current activated by depolarization that had an initial inward and a later outward component.5. After EGTA was injected into an inner segment the outward component was suppressed. Cobalt then blocked an inward current. This current is believed to be carried predominantly by calcium. The conductance increased with depolarization from -45 mV and reached a maximum at approximately 0 mV. Following a step of depolarization the current activated rapidly (< 20 msec) and then remained constant for at least several seconds without evidence of inactivation.6. Injecting caesium into an inner segment eliminated a calcium-activated outward current believed to be carried by potassium ions.7. After the injection of caesium there remained another calcium-activated current with a reversal potential of -17 mV. Changing extracellular chloride concentration altered the value of the reversal potential in a manner consistent with chloride carrying at least 70% of the current. Another anion may carry the balance.8. When the five currents mentioned in items 2, 3, 5, 6 and 7 were blocked, the membrane resistance between -90 and -25 mV was linear, time-independent, and had a high value (2.1 GOmega).9. The five identified currents can all be activated in the physiological range of voltage in which salamander rods normally operate.

Action Potentials↗