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At least 1,009 records · Page 56Linked to original sources
PubMed1991

Activation of the sensory current in salamander olfactory receptor neurons depends on a G protein-mediated cAMP second messenger system.

Olfactory receptor neurons respond to odor stimulation with an inward cationic current. Under whole-cell patch clamp, individual, isolated olfactory receptors were exposed to pharmacological agents known to interact with distinct enzymes in a putative second messenger cascade, and their response to odors was measured. IBMX prolonged the odor-evoked current and also reduced its amplitude. cAMP and cGMP induced a current electrically identical to the odor current, but the current showed desensitization only with cAMP. GTP-gamma-s prolonged and GDP-beta-s interfered with the odor-evoked current. The long latency seen in the odor response appears to be mainly due to the loading of the G protein and secondarily to the requirement for cAMP accumulation. The main source of the response decay appears to be cyclic nucleotide hydrolysis.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Signal transfer from photoreceptors to bipolar cells in the retina of the tiger salamander.

Under conditions of dark-adaptation, in response to weak stimuli, the distal retina behaves as a linear system. During the process of voltage transfer from the rods to the bipolar cells the information encoded in the rod responses is spatially filtered. The spatial filtering is determined by the spatial properties of the receptive field of the bipolar cell. These, in turn, depend upon the spatial properties of three syncytia, those of the receptors, the horizontal cells and the bipolar cells themselves. The response of the bipolar cell to these weak stimuli is a linear difference of two components; a component generated by the receptive field center and a component generated by the receptive field surround. The receptive field surround is misnamed since it extends throughout the receptive field center and contributes to the response of the bipolar cell to stimuli located anywhere within the receptive field. The receptive field surround has the spatial properties that would be expected if it were generated by an input from the horizontal cells to the receptive field center of the bipolar cell. The cellular pathway mediating this input remains unclear though we have evidence that it involves, at least in part, a feedforward pathway from horizontal cells to bipolar cells. If a feedback pathway also exists it is not mediated by the GABAA synapse on the synaptic terminals of the cones.

Animals↗
PubMed2000

Anion modulation of calcium current voltage dependence and amplitude in salamander rods.

Hofmeister anions were used to investigate the ability of Cl(-) replacement to produce inhibition and a hyperpolarizing activation shift in L-type Ca(2+) currents (I(Ca)) of rod photoreceptors. Inhibition of I(Ca) largely followed the Hofmeister sequence: Cl(-)=Br(-)<NO(-)(3)<I(-)<ClO(-)(4) (ClO(-)(4) caused the greatest suppression). Anion-induced hyperpolarizing activation shifts also followed the Hofmeister sequence: Cl(-)<Br(-)<NO(-)(3)<I(-)<ClO(-)(4) (ClO(-)(4) caused the largest shift). Agreement with the Hofmeister sequence suggests that these effects are due to anion interactions at the membrane surface. Hofmeister anions also caused similar hyperpolarizing shifts in the voltage dependence of inwardly rectifying cation currents (I(h)) and outward K(+) currents (I(K)) consistent with the hypothesis that hyperpolarizing shifts arise from anion effects on membrane surface potential. Sulfate and phosphate inhibited rod I(Ca) and phosphate caused a significant leftward activation shift suggesting these anions are strongly adsorbed to the membrane. Because of the overlap between the physiological voltage range and the lower part of the I(Ca) activation curve, anion effects on amplitude and activation may influence synaptic transmission at the first retinal synapse.

Animals↗
PubMed1993

Diffusion coefficient of cyclic GMP in salamander rod outer segments estimated with two fluorescent probes.

Experiments have demonstrated that single photoisomerizations in amphibian and primate rods can cause the suppression of 3-5% of the dark circulating current at the response peak (Baylor, D. A., T. D. Lamb, and K. W. Yau. 1979. J. Physiol. (Lond.). 288:613-634; Baylor, D. A., B. J. Nunn, and J. L. Schnapf. 1984. J. Physiol. (Lond.). 357:575-607). These results indicate that the change in [cGMP] effected by a single isomerization must spread longitudinally over at least the corresponding fractional length of the outer segment. The effective longitudinal diffusion coefficient, Dx, of cGMP is thus an important determinant of rod sensitivity. We report here measurements of the effective longitudinal diffusion coefficients, Dx, of two fluorescently labeled molecules: 5/6-carboxyfluorescein and 8-(fluoresceinyl)thioguanosine 3',5'-cyclic monophosphate, introduced into detached outer segments via whole-cell patch electrodes. For these compounds, the average time for equilibration of the entire outer segment with the patch pipette was approximately 6 min. Fluorescence images of rods were analyzed with a one-dimensional diffusion model that included limitations on transfer between the electrode and outer segment and the effects of intracellular binding of the dyes. The analyses yielded estimates of Dx of 1.9 and 1.0 microns 2.s-1 for the two dyes. It is shown that these results place an upper limit on Dx for cGMP of 11 microns2.s-1. The actual value of Dx for cGMP in the rod will depend on the degree of intracellular binding of cGMP. Estimates of the effective buffering power for cGMP in the rod at rest range from two to six (Lamb and Pugh, 1992; Cote and Brunnock, 1993). When combined with these estimates, our results predict that for cGMP itself, Dx falls within the range of 1.4-5.5 microns 2.s-1.

Ambystoma↗
PubMed1999

Crystallographic and chemical composition of otoconia in the salamander Pleurodeles waltl.

The aim of the present study was to define the morphology and the crystallographic and chemical composition of otoconia in different regions of the inner ear in Pleurodeles waltl (urodele amphibian). The inner ear of adults was microdissected and otoconia were analyzed by scanning electron microscopy (SEM), X-ray diffraction, energy dispersive X-ray (EDX) and transmission electron microscopy. Two types of crystals were detected by SEM. Otoconia had different shapes depending on their location in the membranous labyrinth. One type had a cylindrical body with a triplanar smooth facet at each end, the other ones had either a prismatic shape with flat sides and end faces or a fusiform shape with rounded body and pointed end. The forms corresponded to those previously identified by other authors. These two types of otoconia had different X-ray diffraction patterns. The cylindrical otoconia were calcitic and located in the utricle, the other ones were aragonitic and located in the saccule, lagena and endolymphatic sac. An analysis by EDX indicated that both types of otoconia contained about 95% calcium with trace quantities of sodium, magnesium, phosphorus, sulfur, chlorine and potassium. Trace amounts of strontium was only found in the aragonitic otoconia.

Animals↗
PubMed2000

Development of the pattern of dentition and dental laminae of Costa Rican plethodontid salamanders (Amphibia: Urodela).

The pattern of development of teeth and dental laminae of three Costa Rican plethodontids (Amphibia, Urodela, Plethodontidae) was investigated using transparent preparations, light microscopy and scanning electron microscopy. The teeth of the jaws are monostichously positioned, those of the posterior vomeral parts are polystichously arranged. The anterior vomeral parts carry monostichously positioned teeth at the caudal margin; yet, the adult Bolitoglossa subpalmata possesses two lines. As a sex dimorphism adult males display long monocuspid premaxillary teeth which protrude to the outside of the mouth cavity. All species studied possess paired dental laminae in the lower jaw. Nototriton abscondens possesses an unpaired dental lamina in the upper jaw, which is constricted between the unpaired premaxillary and the maxillaries. In contrast, the dental laminae in the upper jaw of B. subpalmata and Oedipina uniformis are segmented into a premaxillary and two maxillary laminae. All species possess a pair of anterior vomeral and a pair of posterior vomeral dental laminae in the adults, whereas the vomeral dental laminae of the subadults are unsegmented. The pattern of dentition is compared with that of Gyrinophilus and Eurycea.

Aging↗