Slow motility in hair cells of the frog amphibian papilla: Myosin light chain-mediated shape change

Farahbakhsh, Afshin; Narins, Peter M.

doi:10.1016/j.heares.2008.04.007

Cited by 4 publications

(6 citation statements)

References 52 publications

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“…In summary, while a high concentration of HgCl 2 produces a shape change in APHCs that is somewhat reminiscent of that induced by ionomycin (Farahbakhsh and Narins, 2006, 2008), its effects on the osmotically-evoked shape change and on the permeability to water in these cells are not statistically significant.…”

Section: Resultsmentioning

confidence: 82%

“…Our measurements indicate that confocal microscope distorted these images (see Fig. 1E), causing a 20% overestimation in the calculated volume, which appeared to be independent of the bead or cell size (Farahbakhsh and Narins, 2008). However, because of an even larger overestimation of the surface area by the confocal microscope, the ratio of volume/surface area ( V/A ) estimated by the 3-D reconstruction software (Volocity) is about 13% smaller than that calculated on the basis of our cell model (Fig.…”

Section: Methodsmentioning

confidence: 84%

“…In two recent reports (Farahbakhsh and Narins, 2006, 2008), we described a calcium-dependent mechanism that can potentially mediate the process of slow motility in low-frequency auditory hair cells of amphibians. Furthermore, we developed a method for quantitative analysis of shape change in isolated hair cells and devised a model for identifying different aspects of the response to agents that modulate the geometrical attributes of these cells.…”

Section: Introductionmentioning

confidence: 99%

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Osmotic properties of auditory hair cells in the leopard frog: Evidence for water-permeable channels

2011

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When amphibian papillar hair cells (APHCs) of the leopard frog, Rana pipiens pipiens, are osmotically challenged, they exhibit a characteristically asymmetric (rectifying) response: Small decreases (5%, or less) in the extracellular solution’s osmolarity do not significantly affect the cells’ volume; larger decreases produce a relatively slow volume increase in APHCs, while exposure to a hyperosmotic medium leads to rapid shrinking of these cells. Furthermore, the rate of volume change appears to be a function of the rate of extracellular osmotic change. These characteristics make the application of methods devised for the estimation of the osmotic permeability coefficient (Pf) for semipermeable membranes – i.e. those with significant permeability only to water – to APHC membrane rather futile. We have therefore devised a method that takes both the permeability to solutes as well as the kinetics of the osmolarity change into consideration, in order to obtain estimates of Pf that are to a large degree independent of these factors. We have compared the new and earlier methods. Using the new method, we have estimated the Pf of APHCs’ plasma membrane to be in the 10−2-cm/s range, and thus significantly larger than those reported for lipid bilayers. APHC’s membrane Pf appears to be cell-size independent and insensitive to extracellular mercury. These results suggest that APHCs express water-permeable channels in their plasma membrane. Furthermore, we suggest that asymmetric and rate dependent shape changes produced by osmolarity changes in APHCs imply the presence of significant permeability to solutes. The significance of transmembrane solute transport and water channel expression in amphibian auditory hair cells is discussed.

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Section: Resultsmentioning

confidence: 82%

Section: Methodsmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

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Osmotic properties of auditory hair cells in the leopard frog: Evidence for water-permeable channels

2011

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“…An analogous effect evidently occurs on inhibition of MLCK, making the curves similar. The effect of MLCK (decrease in effect on addition of ML-7) on the process of actin-myosin interactions, which, as suggested [17], underlies isovolumic contraction, is seen in frog papillary cells.…”

Section: Discussionmentioning

confidence: 83%

The Role of Myosins in Depression of Neuron Sensitivity to Acetylcholine in a Cellular Analog of Habituation in the Common Snail

Pivovarov

Murzina

Makhnovskii

et al. 2014

Neurosci Behav Physi

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Published data indicate that the synaptic inputs to defensive behavior command neurons in the common snail are cholinergic [6, 10] and glutamatergic [12]. The presence of pharmacologically similar postsynaptic and extrasynaptic cholinoreceptors in command neuron membranes [6,8,10] provides an approach to studying the postsynaptic mechanism of plasticity in command neurons in conditions of artificial activation of extrasynaptic cholinoreceptors, such that uncontrollable changes in transmitter release from the presynapse in conditions of electrical stimulation of the synaptic inputs can be excluded. Local application of constant-size portions of acetylcholine (ACh) to the body surface from an injection micropipette, operating as an artificial presynapse substituting for a presynaptic terminal, results in stable stimulation of a zone of the membrane containing extrasynaptic cholinoreceptors. The stimulation protocol for extrasynaptic cholinoreceptors imitates the stimulation scheme inducing habituation of the animal's defensive reactions [5]. Rhythmic application of ACh in these conditions leads to reversible depression of the evoked influx current (the ACh current), which reflects a decrease in the ACh sensitivity of the membrane [5].We have previously demonstrated that depression of the cholinosensitivity of the extrasynaptic zones of defensive behavior command neuron membranes in the common snail in a cellular analog of habituation results from a decrease in the number of membrane cholinoreceptors in the test zone [4]. Transport processes (endocytosis and exocytosis, underlying the internalization and recycling of receptors respectively) mediate these changes on the somatic membranes of neurons, with involvement of cytoskeletal elements, i.e., The involvement of cytoskeletal motor proteins, i.e., myosins, in the molecular mechanism of depression of the acetylcholine sensitivity of defensive behavior command neurons was studied in the common snail. Thus, the effects of compounds impairing myosin functioning on ACh-evoked current depression curves in neurons were studied -the myosin light chain kinase blockers ML-7 and MLCK-IP-18, the non-muscle myosin II inhibitor blebbistatin, and the ROCK-I and ROCK-II kinase (which mainly activate non-muscle myosin II) inhibitor Y-27632. ML-7 and MLCK-IP-18 were found to weaken depression of the current, while blebbistatin and Y-27632 had no effect on depression. The experimental results and mathematical models of the effects of these blockers on the number of membrane-bound cholinoreceptors suggest the involvement of myosins (except non-muscle myosin II) in the endo-and exocytosis of cholinoreceptors and the resultant depression of the cholinosensitivity of the somatic membranes of neurons in a cellular analog of habituation.

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“…AP hair cells change their cell volume in response to hyper- and hypo-osmotic media and these osmolarity-induced changes are insensitive to mercury. Additionally, AP hair cells possess a calcium-calmodulin-dependent slow motility mechanism, which is temporarily accompanied by volume change (Farahbakhsh and Narins, 2006, 2008). The ability of amphibian hair cells to change their volume in an iso-osmotic medium suggests that they may have mechanisms for transporting solutes and water across the cell membrane.…”

Section: Introductionmentioning

confidence: 99%

Evidence for water-permeable channels in auditory hair cells in the leopard frog

et al. 2012

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Auditory hair cells in the amphibian papilla (APHCs) of the leopard frog, Rana pipiens pipiens, have a significantly higher permeability to water than that observed in mammalian hair cells. The insensitivity of water permeability in frog hair cells to extracellular mercury suggests that an amphibian homologue of the water channel aquaporin-4 (AQP4) may mediate water transport in these cells. Using immunocytochemistry, we show that an AQP4-like protein is found in APHCs. Rabbit anti-AQP4 antibody was used in multiple-immunohistochemical staining experiments along with AP hair cell and hair bundle markers in leopard frog and mouse tissue. AQP4-immunoreactivity was found in the basal and apical poles of the APHCs and shows uniform immunoreactivity. This study provides the first identification and localization of an AQP4-like protein in the amphibian inner ear. We also report a more direct measure of hyperosmotically-induced volume changes in APHCs that confirms previous findings. The presence of water channels in anuran APHCs constitutes a novel physiological difference between amphibian and mammalian hair cell structure and function.

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Slow motility in hair cells of the frog amphibian papilla: Myosin light chain-mediated shape change

Cited by 4 publications

References 52 publications

Osmotic properties of auditory hair cells in the leopard frog: Evidence for water-permeable channels

Osmotic properties of auditory hair cells in the leopard frog: Evidence for water-permeable channels

The Role of Myosins in Depression of Neuron Sensitivity to Acetylcholine in a Cellular Analog of Habituation in the Common Snail

Evidence for water-permeable channels in auditory hair cells in the leopard frog

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