Biology subjects

Alonso, R. G.

Publications and source records attributed to Alonso, R. G..

2 recordsLinked to original sources

bioRxiv2023

Influence of myosin regulatory light chain and myosin light chain kinase on hair cells of the inner ear

In the receptor organs of the inner ear and lateral line, sensory hair cells detect mechanical stimuli such as sounds, accelerations, and water movements. In each instance a stimulus deflects the hair bundle, a hair cells mechanically sensitive organelle. The bundle pivots upon the cells apical surface, which includes an actin meshwork called the cuticular plate and is surrounded by a ring of filamentous actin and non-muscle myosin II (NM2). Myosin regulatory light chain (RLC) is expressed at the apical surfaces of hair cells and RLC is additionally found in hair bundles. NM2 and the phosphorylation of RLC by myosin light chain kinase (MLCK) have earlier been shown to regulate the sizes and shapes of hair cells apical surfaces. We have found that inhibitors of NM2 and MLCK reduce the stiffness of hair bundles from the bullfrogs sacculus. Moreover, MLCK inhibition inhibits the spontaneous oscillation of hair bundles and increases the resting open probability of transduction channels. In addition, MLCK inhibition elevates hearing thresholds in mice. We conclude that NM2 and the phosphorylation of RLC modulate slow adaptation and thereby help to set the normal operating conditions of hair bundles. Statement of significanceSensory hair cells play a key role in mechanoelectrical transduction by the inner ear and lateral-line system. To detect stimuli such as sounds and accelerations, hair cells use an active process to amplify their mechanical inputs. Although amplification is accomplished in part by the activity of the mechanosensitive hair bundles, the molecular mechanism of the active process remains uncertain. The present study shows that non-muscle myosin II (NM2) and the phosphorylation of myosin regulatory right chains (RLC) by myosin light chain kinase (MLCK) regulate the stiffness and spontaneous oscillation of hair bundles as well as the resting open probability of mechanotransduction channels. The results implicate myosin motors in the control of the active process of hair cells.

biophysics↗

bioRxiv2020

Fast recovery of disrupted tip links induced by mechanical displacement of hair bundles

Hearing and balance rely on the capacity of mechanically sensitive hair bundles to transduce vibrations into electrical signals that are forwarded to the brain. Hair bundles possess tip links that interconnect the mechanosensitive stereocilia and convey force to the transduction channels. A dimer of dimers, each of these links comprises two molecules of protocadherin 15 (PCDH15) joined to two of cadherin 23 (CDH23). The "handshake" that conjoins the four molecules can be disrupted in vivo by intense stimulation and in vitro by exposure to Ca2+ chelators. Using hair bundles from the rats cochlea and the bullfrogs sacculus, we observed that extensive recovery of mechanoelectrical transduction, hair-bundle stiffness, and spontaneous bundle oscillation can occur within seconds after Ca2+ chelation, especially if hair bundles are deflected towards their short edges. Investigating the phenomenon in a two-compartment ionic environment that mimics natural conditions, we combined iontophoretic application of a Ca2+ chelator to selectively disrupt the tip links of individual frog hair bundles with displacement clamping to control hair-bundle motion and measure forces. Our observations suggest that, after the normal Ca2+ concentration has been restored, mechanical stimulation facilitates the reconstitution of functional tip links. Significance StatementEach of the sensory receptors responsible for hearing or balance--a hair cell--has a mechanosensitive hair bundle. Mechanical stimuli pull upon molecular filaments--the tip links--that open ionic channels in the hair bundle. Loud sounds can damage hearing by breaking the tip links; recovery by replacement of the constituent proteins then requires several hours. We disrupted the tip links in vitro by removing the calcium ions that stabilize them, then monitored the electrical response or stiffness of hair bundles to determine whether the links could recover. We found that tip links recovered within seconds if their ends were brought back into contact. This form of repair might occur in normal ears to restore sensitivity after damage.

neuroscience↗