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B Oakley

Publications and source records attributed to B Oakley.

70 records · Page 4Linked to original sources
PubMed1978

The electrogenic sodium pump of the frog retinal pigment epithelium.

It was previously shown that ouabain decreases the potential difference across an in vitro preparation of bullfrog retinal pigment epithelium (RPE) when applied to the apical, but not the basal, membrane and that the net basal-to-apical Na+ transport is also inhibited by apical ouabain. The suggested the presence of a Na+ - K+ pump on the apical membrane of the RPE. In the present experiments, intracellular recordings from RPE cells show that this pump is electrogenic and contributes approximately - 10 mV to the apical membrane potential (VAP). Apical ouabain depolarized VAP in two phases. The initial, fast phase was due to the removal of the direct, electrogenic component. In the first one minute of th response to ouabain, VAP depolarized at an average rate of 4.4 +/- 0.42 mV/min (n = 10, mean +/- SEM) and VAP depolarized an average of 9.6 +/- 0.5 mV during the entire fast phase. A slow phase of membrane depolarization, due to ionic gradients running down across both membranes, continued for hours at a much slower rate, 0.4 mV/min. Using a simple diffusion model and K+-specific microelectrodes, it was possible to infer that the onset of the ouabain-induced depolarization coincided with the arrival of ouabain molecules at the apical membrane. This result must occur if ouabain affects an electrogenic pump. Other metabolic inhibitors, such as DNP and cold, also produced a fast depolarization of the apical membrane. For a decrease in temperature of congruent to 10 degrees C, the average depolarization of the apical membrane was 7.1 +/- 3.4 mV (n = 5) and the average decrease in transepithelial potential was 3.9 +/- 0.3 mV (n = 10). These changes in potential were much larger than could be explained by the effect of temperature on an RT/F electrodiffusion factor. Cooling the tissue inhibited the same mechanism as ouabain, since prior exposure to ouabain greatly reduced the magnitude of the cold effect. Bathing the tissue in 0 mM [K+] solution for 2 hr inhibited the electrogenic pump, and subsequent re-introduction of 2 mM [K+] solution produced a rapid membrane hyperpolarization. We conclude that the electrogenic nature of this pump is important to retinal function, since its contribution to the apical membrane potential is likely to affect the transport of ions, metabolites, and fluid across the RPE.

Animals↗
PubMed1978

Effect of intracellular potassium upon the electrogenic pump of frog retinal pigment epithelium.

We have studied the hyperpolarizing, electrogenic pump located on the apical membrane of the retinal pigment epithelium (RPE) in an vitro preparation of bullfrog RPE-choroid. Changes in RPE [K+]i alter the current produced by this pump. Increasing [K+]o in the solution perfusing the basal membrane increases RPE [K+]i (measured with a K+-specific microelectrode), and also depolarizes the apical membrane. The depolarization is due to a decrease in electrogenic pump current flowing across the apical membrane resistance, since it is abolished when the pump is inhibited by apical ouabain, by cooling the tissue, or by 0 mM [K+]o outside the apical membrane. Removal of Cl- from the solution perfusing the basal membrane abolishes the K+-evoked apical depolarization by preventing the entry of K+ (as KCl) into the cell. We conclude that the increase in [K+]i causes the decrease in pump current. This result is consistent with the finding that [K+]i is a competitive inhibitor of the Na+ - K+ pump in red blood cells. It is possible that the light-evoked changes in [K+]o in the distal retina could alter RPE [K+]i, and thus could affect the pump from both sides of the apical membrane. Any change in pump current is likely to influence retinal function, since this pump helps to determine the composition of the photoreceptor extracellular space.

Animals↗
PubMed1977

Regeneration of fungiform taste buds: temporal and spatial characteristics.

The gross morphology of the tongue of the Mongolian gerbil Meriones unguiculatus), the location of papillae and taste buds, and the normal innervation pattern of the tongue and taste buds were determined. The chorda tympani nerve was interrupted to produce degeneration of fungiform taste buds. Regenerating chorda tympani axons followed the original nerve pathways in the tongue en route to the fungiform papillae in the epithelium where they initiated the regeneration of taste buds. The spatial distribution of reinnervated fungiform papillae and reformed taste buds was examined 7 to 19 days following surgery. Beginning at eight days following chorda tympani interruption there was a progressive increase, first, in the proportion of fungiform papillae that were reinnervated, and later in the number of reformed taste buds. On the basis of these measures it was concluded that a taste bud is reformed one to two days after reinnervation of its papilla. From the time course of reinnervation of the fungiform papillae it was calculated that some fibers regenerated at rates in excess of 2 mm/day. Regeneration was precise and systematic. The regenerating chorda tympani fibers accurately returned to the fungiform papillae; they did not follow the pathways of lingual nerve axons. In the initial stages of recovery both reinnervated papillae and reformed taste buds were preferentially located toward the front of the tongue; the reinnervation of posterior fungiform papillae was delayed.

Animals↗
PubMed1977

Taste fiber responses during reinnervation of fungiform papillae.

Crushing or transecting the chorda tympani nerve of the gerbil (Meriones unguiculatus) caused ipsilateral degeneration of taste buds in the fungiform papillae. In less than two weeks some taste fibers regenerated into the tongue and formed new taste buds and receptor cells. The recovery process was evaluated electrophysiologically in 53 gerbils by acute recording proximal to the nerve injury site. Initially the chorda tympani was electrically silent. In gerbils tested at later times spontaneous activity appeared. This was followed by responses to pressure on the tongue. Taste responses returned as early as day 11. The receptive field of regenerated taste fibers was limited to a small number of fungiform papillae. Taste responses were always associated with the presence of one or more taste buds in the receptive field. Taste buds identified as responsive to chemicals contained some fusiform cells. We found that the taste responses of single fiber, few-fiber and multi-unit preparations reflected the diversity of responses found in normal taste axons as determined by recording from 26 normal single fibers and 27 normal whole nerves. The early emergence of a variety of fiber types and responses to many chemicals in regeneration is inconsistent with the proposition that the relative chemical responsiveness of a receptor cell is strictly a function of its age; the response of a given young taste receptor is not necessarily limited to a few of the standard taste stimulants.

Animals↗
PubMed1977

Potassium and the photoreceptor-dependent pigment epithelial hyperpolarization.

Light-evoked changes in pigment epithelial cell membrane potentials and retinal extracellular potassium ion concentration, [K+]0, were measured in an in vitro frog retina-pigment epithelium-choroid preparation. Light stimuli hyperpolarized the apical membrane of the pigment epithelium. Through an electrical shunt pathway connecting the apical and basal membranes, the basal membrane also hyperpolarized, but to a lesser degree than the apical membrane. This differential hyperpolariation of the two membranes increased the transepithelial potential (TEP). This increase in TEP was shown to be the major voltage source of the c-wave of the electroretinogram (ERG). Direct measurement of [K+]0 in the distal retina, made with K+-specific microelectrodes, showed a light-evoked decrease in [K+]0 having an identical time course to the apical hyperpolarization. There was a linear relationship between the light-evoked change in TEP and the logarithm of [K+]0. This exact relationship was also found when the apical membrane was perfused directly with solutions of varying [K+]0. The change in TEP associated with the ERC c-wave, therefore, was explained solely by the response of the pigment epithelium to the light-evoked decrease in [K+]0 in the distal retina.

Animals↗
PubMed1977

The in vitro frog pigment epithelial cell hyperpolarization in response to light.

Pigment epithelial cell membrane potentials were measured in an in vitro frog retina-pigment epithelium-choroid preparation. Light stimuli hyperpolarized the apical membrane of the pigment epithelium. This hyperpolarization was the source of the c-wave of the electroretinogram. Light stimuli also decreased retinal extracellular potassium ion concentration, [K+]O, with the same time course as the apical hyperpolarization. It is suggested that the pigment epithelial hyperpolarization, which causes the c-wave, results directly from the light-evoked decrease in retinal [K+]O.

Animals↗
PubMed1976

Stimulation of the gerbil's gustatory receptors by polyols.

The gustatory responses of the Mongolian gerbil were tested with 12 sugar alcohols. The electrophysiological effectiveness of the linear polyols as gustatory stimulants increased as the length of the carbon chain increased from 2 to 5. Six and 7 carbon acyclic polyols were no more effective than the pentitols. By comparison myoinositol, a cyclic polyol, was more effective in evoking a response. Responses to mixtures of D-sorbitol and sucrose suggest that these sugars compete for a common receptor site. A sucrose receptor site and a model of it is proposed.

Animals↗
PubMed1976

Correlation of light-induced changes in retinal extracellular potassium concentration with c-wave of the electroretinogram.

1. Double-barrel, potassium-specific microelectrodes have been used to measure light-induced transient changes in [K+]o in the frog eye cup preparation. These changes in [K+]o have been termed the potassioretinogram (KRG). 2. The KRG consists of two components: a rapid increase in [K+]o in the proximal retina and a slow decrease in [K+]o in the distal retina. 3. The KRG decrease has the rhodopsin action spectrum, is maximal in the photoreceptor layer, persists after aspartate treatment, and has an increment threshold curve which saturates at moderate background intensities. The rhodopsin rods are, therefore, most likely the only neurons which generate this ionic change, although the Müller (glial) cells may also be involved in this process. 4. The KRG decrease has the same time course as the c-wave of the electroretinogram for all variations in the stimulus parameters, including intensity, duration, and chromaticity. 5. It is suggested that the c-wave may be produced by the pigment epithelial cells as they hyperpolarize in response to the decrease in [K+]o around the photoreceptors.

Animals↗
PubMed1967

Altered temperature and taste responses from cross-regenerated sensory nerves in the rat's tongue.

1. The chorda tympani nerve, which innervates the front of the rat tongue, was found to be much less responsive to tongue cooling than the IXth nerve, which innervates the back of the tongue. The two nerves also differed in their relative responsiveness to various taste chemicals.2. Through cross-union the IXth nerve was made to innervate the front of the tongue, and in other rats the chorda tympani nerve the back of the tongue.3. After an average of 15 post-operative weeks, electrophysiological recordings of whole nerve action potential discharges were made from normal, control regenerated, and cross-regenerated nerves. Cooling, and chemical and mechanical stimulation of the tongue demonstrated that the control regenerated and cross-regenerated nerves had established functional connexions.4. Neither the response to cooling nor the relative taste responses were altered by either of two types of control chorda tympani nerve regeneration.5. In contrast, the cross-regenerated chorda increased its responsiveness to tongue cooling and the cross-regenerated IXthe nerve lost much of its responsiveness to cooling.6. Cross-regeneration also caused the relative taste responses to change and appear quite similar to the responses obtained from the nerve which normally innervated that tongue region (e.g. the cross-regenerated IXth nerve responded like a chorda tympani nerve).7. It is suggested that the sensory response evoked in the chorda tympani and IXth nerves by tongue cooling or taste stimulation is at least partially dependent upon the character of the tongue tissue in which the nerve terminates-the epithelium at the front differs from that at the back of the rat tongue.8. These results rule out the following two hypotheses: (a) that the nerve ending itself functions as a taste receptor in direct contact with applied chemicals and yet is uninfluenced by the character of the tissue in which it terminates, (b) that assuming the taste bud cells are an integral part of the receptive process, the taste nerve ending determines the chemical specificity of the taste cell which it induces, without any previous modification of the nerve by the tissue in which it terminates.

Action Potentials↗
PubMedDate not supplied

Injection of GTP-binding protein or cyclic GMP phosphodiesterase hyperpolarizes retinal rods.

Light-induced activation of cyclic GMP phosphodiesterase (PDE) in the outer segments of vertebrate rod photoreceptors has been suggested as a step in the transduction process linking the absorption of light by rhodopsin with a hyperpolarization of the plasma membrane. Activation of PDE is mediated by a 'GTP-binding protein' (G). As a result of interaction with a rhodopsin photoproduct (possibly metarhodopsin II380), this GTP-binding protein exchanges a previously bound GDP for a GTP. This 'GTP-charged' protein (GGTP) is thought to activate PDE through an interaction in which an inhibitory protein is released from PDE. Assays of PDE activity in vitro have demonstrated that the hydrolysis of cyclic GMP occurs within milliseconds of light onset, which suggests that this process is rapid enough to be an intermediate step in transduction. To test this idea electrophysiologically, we have injected purified GTP-binding protein that was binding a hydrolysis-resistant analogue of GTP, guanylyl imidodiphosphate (p(NH)ppG), termed Gp(NH)ppG, as well as partially purified PDE, into toad rod outer segments while recording membrane voltage. We report here that injection of either of these biochemically active proteins induces a reversible hyperpolarization of the rod membrane, while injection of inactive proteins seems to have no effect on membrane voltage.

3',5'-Cyclic-GMP Phosphodiesterases↗