Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SALAMANDERS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed1996

The action of cytoplasmic calcium on the cGMP-activated channel in salamander rod photoreceptors.

1. Truncated salamander rod photoreceptors were internally perfused to investigate the action of cytoplasmic Ca2+ on cGMP-activated channels in the outer segment. 2. Switching from 1 microM Ca2+ to 0 Ca2+ increased the cGMP-activated current by a factor of 7.1 +/- 0.5 when measured in the first 60 s after the outer segment was opened to the bath, but only 2-fold after 5 min or more. This was attributed to the loss from the outer segment of a soluble factor required for Ca2+ to inhibit the cGMP-activated channel. 3. Short exposures to 0 Ca2+ caused an irreversible increase in the cGMP-activated current measured in 1 microM Ca2+, indicating that lowering [Ca2+] accelerated the loss of the channel inhibitor from the outer segment. 4. Channel activation occurred with a half-time of 6.7 s on switching to 0 Ca2+. Replacing 1 microM Ca2+ inhibited the current again with a half-time of 11.0 s. 5. The inhibition of the cGMP-activated current by Ca2+ could be described by a Hill curve with half-maximal suppression at 55 +/- 13 nM Ca2+ and a Hill coefficient of 1.4 +/- 0.4. 6. Addition of calmodulin (1 microM), or the calmodulin inhibitors mastoparan and calmidazolium (5 microM), did not alter the action of Ca2+ on the cGMP-activated current. 7. The increased affinity of the cGMP-activated channels in response to a fall in [Ca2+] has the magnitude, speed and Ca2+ dependence to suggest that it will promote recovery of the cGMP-activated current in response to the light-induced fall in [Ca2+] that normally occurs inside the outer segment.

Ambystoma↗
PubMed1997

Regulation of intracellular pH in salamander retinal rods.

1. We measured intracellular pH (pHi) in rods isolated from the retina of the axolotl salamander, Ambystoma mexicanum, using the fluorescent indicator 2',7'-bis(carboxyethyl)-5(and -6)-carboxyfluorescein (BCECF). 2. The light exposures associated with data acquisition had no marked effect on pHi. There was no sharp change between the value obtained from the first exposure of dark-adapted rods and subsequent readings. Increasing the acquisition frequency from 1 to 10 min-1 either had no effect, or brought about a slow acidification, which was stopped or reversed when the low frequency was restored. 3. In nominally HCO3(-)-free solution at pH 7.5, the rods had a steady-state pHi of 7.09 +/- 0.02 (n = 46) and a buffering power (beta i) of 24 +/- 1 mM (pH unit)-1 (n = 48). The buffering power was virtually constant in the pH range 6.6-8.0. In the same range, pHi dependent linearly on perfusion pH (pHo) with regression coefficients of 0.4-0.5. 4. There were no significant differences between the inner and outer segment of intact rods as regards steady-state pHi or responses to experimental treatments. 5. Recovery from an intracellular acid load imposed by sodium propionate or an NH4Cl prepulse in nominally bicarbonate-free perfusate was completely blocked by decreasing the extracellular Na+ concentration to 7 mM, and slowed by 86% by applying 1 mM amiloride. 6. Introduction of 2% CO2-13 mM HCO3- caused an alkalinization that was often preceded by a transient acidification. Steady-state pHi was on average 0.1 pH units higher than in nominally bicarbonate-free solution. The mean acid extrusion rate, calculated on the assumption that CO2-HCO3- behaves as an open system, was 19% higher (31 +/- 2 mM h-1) than in a solution buffered only by Hepes (26 +/- 2 mM h-1). 7. In the presence of CO2-HCO3-, 100 microM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) decreased the acid extrusion rate by 20% on average. Lowering the extracellular Cl-concentration to 7 mM raised pHi, but did not significantly affect the acid extrusion rate. 8. We conclude that retinal rods regulate pHi by both Na(+)-H+ exchange and mechanism(s) involving HCO3(-)-Cl- exchange. In the present conditions, the Na(+)-H+ exchanger appears as the dominant mechanism for acid extrusion.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2002

Time course and magnitude of the calcium release induced by bright light in salamander rods.

Changes in fluorescence were measured with an argon ion laser from the outer segments of isolated salamander rods containing the Ca(2+)-sensitive fluorescent dye fluo-5F. When the outer segments were exposed to a 0Ca(2+)/0Na(+) solution designed to minimise surface membrane Ca(2+) fluxes, exposure to intense light from the laser evoked a slow increase in fluorescence, reflecting a light-induced rise in outer segment [Ca(2+)](i). The time course of this slow fluorescence rise could be fitted with the sum of two asymptotic exponential functions of approximately equal amplitude, having time constants of approximately 200 ms and 5.7 s. When rods were exposed to saturating background light to reduce outer segment [Ca(2+)](i) before laser illumination, the relative amplitude of the two exponentials was altered so as to reduce the contribution from the one with the shorter time constant. Examination of the initial time course of fluorescence when recording at high temporal resolution revealed a further rapid rise with a time constant of 1-2 ms, which could be observed even from rods in Ringer solution. This initial rapid rise could be abolished by pre-exposing the rod to bleaching illumination, whether the bleach was given in Ringer solution or in 0Ca(2+)/0Na(+) solution. It would therefore appear that the rapid rise in fluorescence is generated in some way by the bleaching of the photopigment. Unlike the slower components of fluorescence increase, the rapid initial rise was virtually unaffected in waveform or amplitude when rods were pre-exposed in Ringer solution to light which was bright enough to suppress completely the circulating current but which bleached a negligible fraction of the photopigment. Furthermore, pre-incubation with the AM ester of the Ca(2+) chelator BAPTA, although completely abolishing the slower components of fluorescence increase, had virtually no effect on the rapid rise. These results indicate that the rapid component, though triggered by rhodopsin bleaching, does not reflect an increase in outer segment [Ca(2+)](i). Neither the rapid nor the slower components of fluorescence increase were affected by exposure of the outer segment to 10 microM of the membrane-permeant compound N,N,N',N'-tetrakis(2-pyridyl-methyl)ethylenediamine (TPEN), which chelates heavy metals such as Zn(2+), or 100 microM 2-aminoethoxydiphenylborate (2-APB), a membrane-permeant blocker of IP(3) receptors. These results appear to exclude a role for changes in heavy metal concentration or Ca(2+) release via IP(3) receptors in the light-induced increases in dye fluorescence. Estimates of absolute Ca(2+) concentration and of rod buffering capacity suggest that the slower components of fluorescence increase represent the release of around 10-50 micromoles Ca(2+) per litre cytoplasmic volume from bound or sequestered stores after bleaching.

Ambystoma↗
PubMed2003

The effect of light on outer segment calcium in salamander rods.

Calcium acts as a second messenger in vertebrate rods, regulating the recovery phase of the light response and modulating sensitivity during light-adaptation. Since light not only decreases the outer segment calcium concentration ([Ca2+]i) by closing cyclic nucleotide-gated channels but can also increase [Ca2+]i by releasing Ca2+ from buffer sites or intracellular stores, we examined in detail the effect of light and circulating current on [Ca2+]i by making simultaneous measurements of suction pipette current and [Ca2+]i from isolated rods of the salamander Ambystoma tigrinum after incorporation of the fluorescent dye fluo-5F. When the release of Ca2+ is measured in 0 Ca2+-0 Na+ solution, minimising fluxes of Ca2+ across the plasma membrane, it is substantial only for light bright enough to bleach a significant fraction of the photopigment and is restricted to the part of the outer segment in which the bleach occurred. It is unlikely, therefore, to make a large contribution to [Ca2+]i for most of the physiological operating range of the rod. Nevertheless, since release is half-maximal for a bleach of less than 10 %, it cannot be produced by a simple mechanism such as a change in the affinity of a binding site on rhodopsin itself but must instead require some more complex interaction. In Ringer solution, the Ca2+ in the light-releasable pool can be discharged merely by the decrease in [Ca2+]i that occurs as the outer segment channels close. In steady background light or after exposure to saturating illumination, the fraction of Ca2+ in the pool decreases essentially in proportion to [Ca2+]i as if Ca2+ were being removed from a buffer site within the cytoplasm. Furthermore, [Ca2+]i itself changes in proportion to the circulating current, with little evidence for a contribution from Ca2+ release or other mechanisms of Ca2+ homeostasis. This indicates that flux of Ca2+ across the plasma membrane is the major determinant of outer segment Ca2+ concentration within the rod's normal operating light intensity range. Once Ca2+ has been discharged from the releasable pool, it is restored following dim illumination apparently as the simple result of the subsequent restoration of dark [Ca2+]i and the rebinding of Ca2+ to its release site, but after brighter light perhaps also as a consequence of regeneration of the photopigment.

Ambystoma↗
PubMed2003

Free magnesium concentration in salamander photoreceptor outer segments.

Magnesium ions (Mg2+) play an important role in biochemical functions. In vertebrate photoreceptor outer segments, numerous reactions utilize MgGTP and MgATP, and Mg2+ also regulates several of the phototransduction enzymes. Although Mg2+ can pass through light-sensitive channels under certain conditions, no clear extrusion mechanism has been identified and removing extracellular Mg2+ has no significant effect on the light sensitivity or the kinetics of the photoresponse. We have used the fluorescent Mg2+ dye Furaptra to directly measure and monitor the free Mg2+ concentration in photoreceptor outer segments and examine whether the free Mg2+ concentration changes under physiological conditions. Resting free Mg2+ concentrations in bleached salamander rod and cone photoreceptor cell outer segments were 0.86 +/- 0.06 and 0.81 +/- 0.09 mM, respectively. The outer segment free Mg2+ concentration was not significantly affected by changes in extracellular pH, Ca2+ and Na+, excluding a significant role for the respective exchangers in the regulation of Mg2+ homeostasis. The resting free Mg2+ concentration was also not significantly affected by exposure to 0 Mg2+, suggesting the lack of significant basal Mg2+ flux. Opening the cGMP-gated channels led to a significant increase in the Mg2+ concentration in the absence of Na+ and Ca2+, but not in their presence, indicating that depolarization can cause a significant Mg2+ influx only in the absence of other permeant ions, but not under physiological conditions. Finally, light stimulation did not change the Mg2+ concentration in the outer segments of dark-adapted photoreceptors. The results suggest that there are no influx and efflux pathways that can significantly affect the Mg2+ concentration in the outer segment under physiological conditions. Therefore, it is unlikely that Mg2+ plays a significant role in the dynamic modulation of phototransduction.

Ambystoma↗
PubMed2004

Desensitization of the mGluR6 transduction current in tiger salamander On bipolar cells.

Light depolarizes retinal On bipolar cells, opening the cation-selective channels that are responsible for producing the synaptic current. In this study, the basic features of light-induced signals were mimicked by bathing slices of salamander retina with an agonist for the mGluR6 receptor that is expressed on the dendrites of On cells, and then displacing the agonist with the mGluR6 antagonist (RS)-a-cyclopropyl-4-phosphonophenylglycine (CPPG). The transduction current that is activated by this protocol rapidly shuts off, or desensitizes. Desensitization was highly correlated with the concentration and the type of Ca2+ buffer that was dialysed into the cell: When Ca2+ buffering was minimized by dialysing cells with 0.5 mM EGTA, the steady-state response was reduced to approximately 40% of the peak response. Buffering with 10 mM EGTA reduced desensitization, while BAPTA completely eliminated it. Removing external Ca2+ also prevented desensitization, suggesting that entry of Ca2+ through the transduction channel provides the trigger. The time course of desensitization was measured by using a voltage jump protocol to rapidly increase Ca2+ influx, and could be fitted with a single time constant on the order of 1 s, in good agreement with previously published rates of desensitization to steps of light in this species. It is proposed that Ca(2+)-dependent shut-off of the On bipolar cell transduction current may contribute to the conversion of sustained to transient light responses that predominate in the inner retina.

Ambystoma↗
PubMed2005

Photoreceptor encoding of supersaturating light stimuli in salamander retina.

In the dark-adapted salamander retina, spikes could be elicited from rods under normal physiological conditions. Spike activity was observed in rods during the recovery phase of the response to saturating light. These action potentials were calcium spikes, blocked by cadmium and L-type calcium channel blockers. In response to light stimuli that saturate the rod peak response, calcium action potentials occurred with a delay that depended on light intensity, with stronger light increasing spike latency. Therefore, these spikes encode rod visual information at light intensities beyond rod saturation. Postsynaptic currents of similar time course were observed in second and third order neurones. Since rods exposed to brighter light stimuli produced more delayed spike activity, these signals might contribute to negative afterimages.

Action Potentials↗
PubMed2005

A comparison of release kinetics and glutamate receptor properties in shaping rod-cone differences in EPSC kinetics in the salamander retina.

Synaptic transmission from cones is faster than transmission from rods. Using paired simultaneous recordings from photoreceptors and second-order neurones in the salamander retina, we studied the contributions of rod-cone differences in glutamate receptor properties and synaptic release rates to shaping postsynaptic responses. Depolarizing steps evoked sustained calcium currents in rods and cones that in turn produced transient excitatory postsynaptic currents (EPSCs) in horizontal and OFF bipolar cells. Cone-driven EPSCs rose and decayed faster than rod-driven EPSCs, even when comparing inputs from a rod and cone onto the same postsynaptic neurone. Thus, rod-cone differences in EPSCs reflect properties of individual rod and cone synapses. Experiments with selective AMPA and KA agonists and antagonists showed that rods and cones both contact pharmacologically similar AMPA receptors. Spontaneous miniature EPSCs (mEPSCs) exhibited unimodal distributions of amplitude and half-amplitude time width and there were no rod-cone differences in mEPSC properties. To examine how release kinetics shape the EPSC, we convolved mEPSC waveforms with empirically determined release rate functions for rods and cones. The predicted EPSC waveform closely matched the actual EPSC evoked by cones, supporting a quantal release model at the photoreceptor synapse. Convolution with the rod release function also produced a good match in rod-driven cells, although the actual EPSC was often somewhat slower than the predicted EPSC, a discrepancy partly explained by rod-rod coupling. Rod-cone differences in the rates of exocytosis are thus a major factor in producing faster cone-driven responses in second-order retinal neurones.

Animals↗
PubMed2006

Calcium channel and glutamate receptor activities regulate actin organization in salamander retinal neurons.

Intracellular Ca2+ regulates a variety of neuronal functions, including neurotransmitter release, protein phosphorylation, gene expression and synaptic plasticity. In a variety of cell types, including neurons, Ca2+ is involved in actin reorganization, resulting in either actin polymerization or depolymerization. Very little, however, is known about the relationship between Ca2+ and the actin cytoskeleton organization in retinal neurons. We studied the effect of high-K+-induced depolarization on F-actin organization in salamander retina and found that Ca2+ influx through voltage-gated L-type channels causes F-actin disruption, as assessed by 53 +/- 5% (n = 23, P < 0.001) reduction in the intensity of staining with Alexa-Fluor488-phalloidin, a compound that permits visualization and quantification of polymerized actin. Calcium-induced F-actin depolymerization was attenuated in the presence of protein kinase C antagonists, chelerythrine or bis-indolylmaleimide hydrochloride (GF 109203X). In addition, phorbol 12-myristate 13-acetate (PMA), but not 4alpha-PMA, mimicked the effect of Ca2+ influx on F-actin. Activation of ionotropic AMPA and NMDA glutamate receptors also caused a reduction in F-actin. No effect on F-actin was exerted by caffeine or thapsigargin, agents that stimulate Ca2+ release from internal stores. In whole-cell recording from a slice preparation, light-evoked 'off' but not 'on' EPSCs in 'on-off' ganglion cells were reduced by 60 +/- 8% (n = 8, P < 0.01) by cytochalasin D. These data suggest that elevation of intracellular Ca2+ during excitatory synaptic activity initiates a cascade for activity-dependent actin remodelling, which in turn may serve as a feedback mechanism to attenuate excitotoxic Ca2+ accumulation induced by synaptic depolarization.

Actins↗
PubMed1962

Response of the neotenic salamander Haideotriton wallacei to a metamorphic agent.

The neotenic, cave-dwelling plethodontid salamander Haideotriton wallacei undergoes only a few minor integumentary changes and loses only a single bone, the coronoid, when treated with sodium laevo thyroxin. Since neither the animal's thyroid nor the supplementary thyroxin is sufficient to effect substantial metamorphosis, genetic factors probably restrict the animal's ability to transform.

Animals↗
PubMed1970

Homing behavior, orientation, and home range of salamanders tagged with tantalum-182.

Using radioactive tags, we recorded movements of salamanders (Plethodon jordani) in their home areas and during homing. Males occupied home areas about three times larger than those of females and made occasional excursions into outlying regions. Homing after 22-to 60-meter displacements was direct and rapid, once initiated. Course headings at 1 meter from release were random; those at 2 meters and more were home-oriented. Males initiated homing movements sooner than females, although both sexes traveled at similar rates. Increased incidence of climbing on vegetation after displacement suggests olfactory mechanisms of orientation. These observations give direct evidence of homing orientation in caudate amphibians.

Animals↗
PubMed1976

Acid precipitation and embryonic mortality of spotted salamanders, Ambystoma maculatum.

Spotted salamanders breed in temporary pools formed in early spring by melted snow and rain. Many of these pools reflect the low pH of precipitation in the northeastern United States. Egg mortality is low (less than 1 percent) in pools near neutrality, but high (greater than 60 percent) in pools more acid than pH 6. Developmental anomalies and the embryonic stage at which death occurs are the same in field situations as at corresponding pH's in laboratory experiments.

Ambystoma↗
PubMed1991

A centromeric satellite DNA in the European plethodontid salamanders (Amphibia, Urodela).

A highly repeated satellite DNA (Hy500) located in the centromeric heterochromatin of the European plethodontid salamander Speleomantes (formerly Hydromantes) was studied. The Hy500 family represents about 1% of the Speleomantes supramontis genome and has a major repeating unit of about 500 base pairs, which may have evolved from the progressive amplification of shorter sequences. This centromeric satellite is conserved in all the Speleomantes species, which nevertheless show distinct patterns of chromosomal distribution, which are of relevance as to their phylogenetic relationships.

Animals↗
PubMed1990

Adenylate cyclase uncoupled beta-adrenergic receptors in salamander proximal tubules.

The isolated perfused proximal tubule of the neotenic salamander Ambystoma tigrinum responds with either a hyperpolarization or depolarization of both the basolateral cell membrane and transepithelial potentials following the addition of 10(-5) M isoproterenol to the bath superfusate. Both responses were blocked by 10(-6) M propranolol but neither response was mimicked by 10(-4) M cAMP. beta-Adrenergic binding studies of individual microdissected proximal tubules using (-)-[3H]CGP-12177 as a hydrophyllic radioligand and (+/-)-timolol (0.1 mM) as the displacer drug revealed two distinct populations of proximal tubules possessing either low (KD = 153.8 nM; Bmax = 110.2 fM/mm) or high affinity (KD = 12.0 nM: Bmax = 3.9 fM/mm) binding characteristics. Competition studies indicated that the bound (-)-[3H]CGP-12177 behaved as a typical beta-adrenergic ligand, being displaced by (-)-isoproterenol but not by (+)-isoproterenol or (-)-phenylephrine. However, neither appeared to be coupled to the adenylate cyclase system. These data suggest the presence of functional beta-adrenergic receptors that do not appear to be coupled to the adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1991

Link between cell apical morphology and H+ secretion in salamander small intestine.

To determine the morphological basis for the cellular secretion of H+ by in vitro salamander jejunum the transepithelial proton flux (JH) was measured under different conditions and compared with the ultrastructure of the villus absorptive cells using transmission electron microscopy in conjunction with morphometric analysis. Norepinephrine (NE) stimulated JH and significantly increased the density of small cytoplasmic vesicular and tubular profiles in the region immediately below the apical plasma membrane of the absorptive cells. Cytoplasmic tubular elements were often observed in direct contact with the plasma membrane at the base of the microvilli, suggesting that expansion of the plasma membrane had occurred. The alpha 2-antagonist, yohimbine, blocked NE-stimulated H+ secretion and reduced the number of tubulovesicles. Theophylline reduced the rate of spontaneous acid secretion and the density of apical tubules and vesicles. Exposure to horseradish peroxidase revealed a physical connection between the extracellular space and the apical tubulovesicular compartment. The direct relationship between the number of apical vesicular and tubular profiles and JH suggests that the luminal membrane plays a fundamental role in the cellular events in H+ secretion. The membranes of the tubules and vesicles may be elements of a dynamic pool of transporting membranes under the control of exogenous effectors such as catecholamines.

Animals↗
PubMed1980

Comparison of transcutaneous permeability in skins of larval and adult salamanders (Ambystoma tigrinum).

The electrical properties and transcutaneous movements of Na, Cl, and water were compared (in vitro) in skins of larval and adult forms of Ambystoma trigrinum. Larval skin had a mean transcutaneous potential difference of 6 mV (inside positive) in adults it was 50 mV. Short-circuit current (Isc) was, respectively, about 2 microA x cm-2 and 20 microA x cm-2. Electrical resistances were similar. Passive effluxes of Na and Cl were similar in both forms but Na influx (active direction) was much greater in the adult. Diffusional permeability to water was less in the larval salamander skin. Influx of Na and Isc were increased by vasotocin in the adult but not larval skin. Water permeability was unaffected by vasotocin in either form. The properties of the premetamorphic skin are compared to those of two other urodele amphibians.

Age Factors↗