Biomedical subjects

R P Bobbin

Publications and source records attributed to R P Bobbin.

At least 37 records · Page 2Linked to original sources

PubMed1996

Acetylcholine response in guinea pig outer hair cells. II. Activation of a small conductance Ca(2+)-activated K+ channel.

The type of K+ channel involved in the acetylcholine (ACh) evoked response (Ksub; sub stands for suberyldicholine) in guinea pig outer hair cells (OHCs) is still uncertain. The present study tests the hypotheses that Ksub is one of the following: a big conductance Ca(2+)-dependent K+ channel (BK), a small conductance Ca(2+)-dependent K+ channel (SK), a KA type of K+ channel, or a Kn type of K+ channel. Patch-clamp technique in the whole-cell mode was used to record from single guinea pig OHCs. ACh (100 microM) was applied to voltage-clamped OHCs and the ACh-induced currents (IACh) were measured. Charybdotoxin (100 nM) had no effect on IACh, while apamin (1 microM) blocked more than 90% of IACh. Lowering the external Ca2+ concentration caused a hyperpolarizing shift of the IACh monitored as a function of the prepulse voltage. Increasing internal Mg2+ (Mgi2+) concentration caused a reduction in the outward IACh without affecting the inward IACh. The Ksub channel was found to be permeable to Cs+. In Cs+ solutions, IACh was 45% of the IACh in K+ solutions. The block of IACh by apamin, the dependence on extracellular Ca2+, the incomplete block of IACh by Cs+, and the ACh-induced Cs+ currents favor the hypothesis that Ksub belongs to the SK type of channels. An ionotropic/nicotinic nature of the ACh mechanism of action is favored. It is suggested that, in vivo, the amplitude of the ACh-induced hyperpolarization may depend on the Ca2+/Mg2+ ratio inside and outside the cell.

Acetylcholine↗

PubMed1996

Differences in cholinergic responses from outer hair cells of rat and guinea pig.

A cholinergic receptor on outer hair cells (OHC) in guinea pig cochlea induces a K+ current when it is activated by acetylcholine and suberyldicholine but not by nicotine or muscarine (Bobbin, 1995). This unusual receptor may contain an alpha 9-subunit. However, the pharmacology of the alpha 9-subunit cloned from rat and expressed in Xenopus oocytes does not completely match that obtained for the ACh receptor in guinea pig OHCs. The response to 1,1-dimethyl-4-phenylpiperazinium (DMPP) is large in guinea pig OHCs and small in oocytes containing receptors of the alpha 9-subunit. Therefore, we compared the effects of cholinergic receptor agonists in rat and guinea pig OHCs using the whole-cell variant of the patch-clamp technique. ACh caused the largest outward K+ current in OHCs from both rat and guinea pig. Carbachol- and suberyldicholine-induced responses were similar in magnitude in OHCs of rat and guinea pig. However, DMPP produced a small response in OHCs from rat and a large response in OHCs from guinea pig. At a concentration of 100 microM, muscarine, oxotremorine M, nicotine and cytisine induced little response in guinea pig OHCs and none in rat OHCs. Results suggest that the ACh receptor on rat OHCs is similar to the alpha 9-subunit-containing receptor expressed in oocytes but different from the ACh receptor on guinea pig OHCs.

Acetylcholine↗

PubMed1996

Chronic low-level noise exposure alters distortion product otoacoustic emissions.

Chen et al. (1995) recently reported an altered response to the application of ATP in outer hair cells (OHC) isolated from guinea pigs continuously exposed for 10 or 11 days to a 65 dB SPL (A-scale) narrow-band noise (1.1-2.0 kHz). The primary goal of the present study was to test the hypothesis that the continuous low-level noise used by Chen et al. (1995) alters cochlear function. Cubic (2f1-f2) and quadratic (f2-f1) DPOAEs, as well as, the amount of contralateral suppression of DPOAE amplitudes were chosen for study. Responses were recorded in urethane-anesthetized guinea pigs with sectioned middle ear muscles. The animals had either been exposed to the low-level noise for 3 or 11 days or not exposed at all (n = 13 animals per group). Results demonstrate that this noise induces frequency-dependent and very localized reductions in 2f1-f2 DPOAE input/output (I/O) functions. However, the f2-f1 DPOAE I/O functions appear to be insensitive to the noise exposure. No noise-related changes were found in the amount of contralateral suppression between the different exposure groups, with the exception of one unexplainable data point (f2-f1 DPOAE = 0.5 kHz; day 3) where it was reduced. The 2f1-f2 DPOAE amplitude alterations lend support to the conclusions of Chen et al. (1995) that chronic low-level noise exposure induces molecular changes in the OHCs which may, in turn, alter cochlear function.

Adenosine Triphosphate↗

PubMed1996

Time-varying alterations in the f2-f1 DPOAE response to continuous primary stimulation. II. Influence of local calcium-dependent mechanisms.

The distortion product otoacoustic emission (DPOAE) corresponding to the frequency f2-f1 displays stereotyped, time-varying amplitude alterations during continuous primary tone stimulation. The origin of these alterations is unknown; however, evidence that efferent neurons contribute little to the changes has been presented (Kujawa et al., 1994a, 1995; Lowe and Robertson, 1995). The present investigation examines the hypothesis that these alterations in f2-f1 amplitude are a reflection of local, Ca(2+)-dependent mechanisms involving the outer hair cell (OHC) response to sustained stimulation. Experiments were performed using urethane-anesthetized guinea pigs with sectioned middle ear muscles. Intracochlear perfusion was employed to reversibly lower perilymph Ca2+ levels and to introduce antagonists and agonists of L-type Ca2+ channels. Manipulations that lowered available Ca2+ (zero Ca2+ artificial perilymph; zero Ca2+ with BAPTA) or that blocked its entry into the cell via L-type Ca2+ channels (nimodipine) reduced, prevented or reversed the perstimulatory changes in f2-f1 DPOAE amplitude. These perilymph manipulations also reduced the overall amplitude of this distortion component while perfusion of an L-type Ca2+ channel agonist (Bay K 8644) increased its amplitude. Mg2+ did not substitute for Ca2+, suggesting that these are not merely divalent cation effects. Results are consistent with the hypothesis that continuous stimulation-related changes in f2-f1 DPOAE amplitude are sensitive to perilymph Ca2+ levels and to the function of L-type Ca2+ channels. However, nimodipine also reduced the endocochlear potential (EP) and Bay K 8644 increased the EP. The sensitivity of both the perstimulatory changes in f2-f1 DPOAE amplitude and the EP to the latter drugs leaves their site(s) of action unresolved.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1995

Time-varying alterations in the f2-f1 DPOAE response to continuous primary stimulation. I: Response characterization and contribution of the olivocochlear efferents.

The f2-f1 distortion product otoacoustic emission (DPOAE) can be observed to undergo gradual alterations in amplitude during continuous ipsilateral stimulation with primary tones. In the present experiments, we characterized the dependence of these amplitude alterations on several stimulus variables (intensity, duration, frequency) and on DPOAE type (quadratic vs cubic) and tested the hypothesis that such alterations are mediated by the olivocochlear (OC) efferents. Responses were recorded in urethane-anesthetized guinea pigs with sectioned middle ear muscles before and after intracochlear application of antagonists (curare, 1 microM; bicuculline, 10 microM; tetrodotoxin, 1 microM) or before and after OC efferent section at the midline of the floor of the IVth ventricle. We confirm previous reports of continuous stimulation-related alterations in the amplitude of the quadratic distortion product, f2-f1, and report a novel, suppressive 'off-effect' apparent in f2-f1 amplitude following a short rest from such stimulation. Response alterations were sensitive to primary intensity and to duration of rest from continuous stimulation, but were not clearly frequency-dependent over the ranges tested. Corresponding alterations in the amplitude of the cubic nonlinearity, 2f1-f2 were very small or absent. Amplitude alterations in f2-f1 were reduced but not blocked by OC efferent antagonists (curare, bicuculline) and were largely unaffected by TTX or by midline brainstem section. All of these manipulations, however prevented completely the known efferent-mediated contralateral sound suppression of both f2-f1 and 2f1-f2 DPOAEs. Taken together, these results do not provide support for efferent control of the f2-f1 amplitude alterations observed during continuous ipsilateral stimulation.

Acoustic Stimulation↗

PubMed1995

ATP modulation of L-type calcium channel currents in guinea pig outer hair cells.

Ca2+ channel currents and their modulation by adenosine 5'-triphosphate (ATP) in acutely isolated guinea pig outer hair cells (OHCs) were investigated using the whole-cell patch-clamp technique. The current-voltage (I-V) relation of OHCs indicated that the Ca2+ channel opened near -30 mV, and the current reached a maximum at +10 and 0 mV in 20 mM Ca2+ and Ba2+ external solutions, respectively. BayK 8644 (BayK, 2 microM) caused a 3.5-fold increase in peak Ca2+ currents and shifted the I-V curves toward more negative potentials. These results suggest that the majority of Ca2+ channels in OHCs have L-type characteristics. The effects of ATP on Ca2+ channels of OHCs were heterogenous. ATP (100 microM) decreased Ca2+ channel currents by 31.7 +/- 5.6% at 0 mV and shifted Ca2+ tail activation curves toward more depolarized potentials in some cells (N = 6). By contrast, in others, ATP enhanced the currents by 43.5 +/- 12.5% at +10 mV (N = 6). In the presence of BayK, however, ATP-induced inhibition or enhancement of Ca2+ channel currents was attenuated. In addition, 100 microM ATP produced little effect on Ca2+ channel currents in another subpopulation of cells (N = 12). This heterogenous neuromodulation of Ca2+ channel currents by ATP may reflect a functional diversity among OHCs.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1995

Nitroprusside suppresses cochlear potentials and outer hair cell responses.

Biochemical and pharmacological evidence supports a role for nitric oxide (NO) in the cochlea. In the present experiments, we tested sodium nitroprusside (SNP), an NO donor, applied by intracochlear perfusions on sound-evoked responses of the cochlea (CM, cochlear microphonic; SP, summating potential; EP, endocochlear potential; CAP, compound action potential) and in vitro on outer hair cell (OHC) voltage-induced length changes and current responses. In vivo application of SNP in increasing concentrations (10, 33, 100, 330 and 1000 microM) reduced all sound-evoked responses starting at about 300 microM. The responses continued to decline after a postdrug wash. At 1 mM SNP decreased EP slowly (approximately 80 min) whereas at 10 mM it reduced EP more rapidly (approximately 20 min). Ferricyanide (1 mM) and S-nitroso-N-acetylpenicillamine (SNAP; 1 mM) had no effect on sound-evoked cochlear potentials. Ferricyanide (1 mM and 10 mM) and ferrocyanide (10 mM) had no effect on EP. In vitro, SNP (10 mM) significantly reduced both OHC voltage-induced length changes and whole-cell outward currents. Results suggest that SNP, possibly acting by released NO, influences cochlear function through effects at the stria vascularis and at the OHCs.

Acoustic Stimulation↗

PubMed1995

Caffeine-induced shortening of isolated outer hair cells: an osmotic mechanism of action.

The application of caffeine to the bathing medium of isolated cochlear outer hair cells (OHCs) induces shortening of the cells (Slepecky et al., 1988). This study was designed to test the hypothesis that a 'smooth muscle-like' mechanism was responsible for the caffeine-induced shortening of OHCs as suggested by Slepecky et al. OHCs were isolated from guinea pig cochleae and length measurements were taken during various drug perfusions. Antagonists of the ryanodine receptor/Ca(2+)-induced Ca2+ release (CICR; tetracaine, ruthenium red, and ryanodine) failed to block the caffeine-induced shortening of the OHCs. Application of the Ca2+ ionophore A23187 caused cell length to increase. These results did not support this hypothesis and therefore, an osmotic mechanism was proposed.

Animals↗

PubMed1995

Evidence that glutathione is the unidentified amine (Unk 2.5) released by high potassium into cochlear fluids.

An unidentified substance, Unk 2.5, may be important in the function of the cochlea. The efflux of Unk 2.5 into cochlear fluids is increased by intense sound (Bobbin and Fallon, 1992) and by exposure of the cochlear tissue to high concentrations of K+ (Bobbin et al., 1990,1991; Bobbin and Fallon, 1992). The unidentified chemical eluted at 2.5 min in chromatograms obtained by HPLC utilizing fluorescence detection and precolumn o-phthalaldehyde (OPA) derivatization of samples of effluent from the cochlea (e.g., Bobbin et al., 1990). The purpose of this investigation was to provide evidence as to the identity of this unidentified chemical we call Unk 2.5. Therefore, we carried out additional HPLC assays on samples obtained during perfusion of the cochlear perilymph compartment. Glutathione (GSH) was found to elute at the same time (@ 2.5 min) as Unk 2.5 in HPLC chromatograms utilizing precolumn derivatization with OPA and mercaptoethanol. In addition, both Unk 2.5 and GSH reacted with OPA without mercaptoethanol present in the reaction mixture to give a peak at 2.5 min in the chromatogram, but failed to show this peak if stored in solutions with a pH > 7 for several days before the reaction. Results indicate that Unk 2.5 is GSH or a closely related compound. Given this probable identification GSH, aka Unk 2.5, has been demonstrated to be released from tissue in the cochlea by high concentrations of K+ (Bobbin et al., 1990,1991) and by intense sound (124 dB SPL; Bobbin and Fallon, 1992).

Acoustic Stimulation↗

PubMed1995

Noise exposure alters the response of outer hair cells to ATP.

The outer hair cells (OHCs) are one target of noise-induced effects. To date there are few studies which examine changes in the function of OHCs induced by noise exposure. There is increasing evidence that ATP may be a neuromodulator acting on OHCs. Therefore, we examined the possibility that the response to ATP may be altered by low-level noise exposure. ATP was tested on cation currents recorded from outer hair cells (OHCs) isolated from chronic noise-exposed guinea pigs and compared to currents recorded from normal control animals. The whole-cell variant of the patch-clamp technique was used. The incidence of response to 100 microM ATP was decreased in OHCs from noise-exposed animals as compared to controls when normal internal and external solutions were employed. When K+ was substituted by N-methyl-glucamine (NMG+) in the pipette solution, there were significant differences in the magnitudes of ATP-evoked currents between cells from noise-exposed and control animals. This was observed in both normal and 20 mM Ba2+ external solutions. In addition, the response to ATP exhibited a dependency on OHC length. In short OHCs (< 65 microns) from noise-exposed animals the magnitude of the response to ATP was significantly reduced. By contrast, the response in long OHCs (> 65 microns) from noise-exposed animals was increased. Results suggest that low-level noise exposure induces changes in OHCs which affect the response of the cell to ATP.

Acoustic Stimulation↗

PubMed1994

Effects of adenosine 5'-triphosphate and related agonists on cochlear function.

Several lines of evidence implicate a neurotransmitter/modulator role for ATP in the cochlea. Most of the work supporting such a notion has been accomplished using in vitro preparations of sensory hair cells or other cochlear tissues. Little is known regarding the functional consequences of ATP receptor activation in vivo. In the present experiments, we tested ATP and related agonist analogs for their effects on sound-evoked responses of the cochlea (cochlear microphonic, CM; summating potential, SP; distortion product otoacoustic emissions, DPOAE) and auditory nerve (compound action potential, CAP) in vivo and on outer hair cell (OHC) currents and cell length in vitro. In vivo, local application of these compounds was associated with concentration- and intensity-dependent response alterations. The slowly-hydrolyzable P2y agonist, ATP-gamma-S, was clearly of greatest in vivo potency: At low to moderate stimulus intensities, micromolar concentrations of this drug reduced all responses, in particular CAP and DPOAEs, which fell to the level of the noise floor. At high intensities, response suppression was smaller and SP was increased. In vivo effects of ATP, ATP-alpha-S and 2-Me-S-ATP were qualitatively similar to, but smaller in magnitude and requiring higher concentrations than those observed for ATP-gamma-S. Adenosine was without significant effect on responses of the cochlea and auditory nerve. In vitro, effects of ATP-gamma-S and ATP were similar: both induced inward currents in OHCs held at -60 mV without producing observable (> 0.3 micron) changes in OHC length. Results suggest that endogenous ATP influences cochlear function through receptors at several sites in the cochlea. Results suggest further that these response alterations are mediated, at least in part, by receptors of the P2y subtype.

Action Potentials↗

PubMed1994

ATP antagonists cibacron blue, basilen blue and suramin alter sound-evoked responses of the cochlea and auditory nerve.

The P2-purinergic receptor antagonists suramin, cibacron blue and basilen blue, the latter two being isomers of reactive blue 2, were studied for their effects on sound-evoked responses from the cochlea (cochlear microphonic, CM; summating potential, SP; distortion product otoacoustic emissions, DPOAE) and auditory nerve (compound action potential, CAP). Local application of these compounds (10-1000 microM) into the cochlear perilymph was associated with concentration-dependent response alterations. Effects of suramin on cochlear responses were minimal: High-intensity SP was reduced slightly at concentrations > or = 330 microM without significant alterations in CM or DPOAEs. The amplitude of the auditory nerve CAP was suppressed and its latency increased at drug concentrations > or = 100 microM. Cibacron blue and basilen blue were of greater potency in their effects on cochlear and auditory nerve responses. DPOAEs were generally reduced, low-intensity SP was reduced and high-intensity SP was increased and CM was little affected at drug concentrations 100-1000 microM. The CAP was suppressed and its latency increased at concentrations > or = 33 microM. Effects of suramin were largely reversible; those associated with cibacron blue and basilen blue generally were not. To the extent that these drugs acted selectively as antagonists of ATP receptor-mediated activity, results support the hypothesis that endogenous ATP exerts profound actions at the level of the cochlea and the auditory nerve.

Action Potentials↗

PubMed1994

Acetylcholine activates a K+ conductance permeable to Cs+ in guinea pig outer hair cells.

Acetylcholine (ACh), the major neurotransmitter released by efferent nerve fibers in the cochlea, has been shown to activate a Ca(2+)-dependent K+ conductance in outer hair cells (OHCs). Previously we reported that this ACh operated conductance is permeable to Cs+. The purpose of the present study was to characterize further this Cs(+)-permeable channel and its dependency on Ca2+ using isolated OHCs and the patch clamp technique in the whole cell configuration. The changes in the ACh response were examined when Cs+, Ba2+, Cd2+, N-methyl-D-glucamine (NMG+) and tetraethylammonium (TEA+) were placed in the external or internal solutions. Cs+ substituted for K+ in carrying the ACh-evoked Ca(2+)-dependent K+ current. When NMG+/TEA+ was substituted for internal K+ ACh-evoked an inward and an outward current, and Cs+ substituted for external K+ blocked the outward but not the inward current evoked by ACh suggesting it was carried by K+. In the NMG+/TEA+ condition, when the cell was held at different Vh values for an extended period of time, the ACh-induced K+ current rectified. In Ba2+ (3 mM) with zero Ca2+ ACh failed to induce any detectable current and the ACh response slowly recovered from the Ba2+ block, suggesting a block at an intracellular site. Cd2+ (1 mM) readily and reversibly blocked ACh-induced currents even when carried by Cs+. This data suggests that ACh opens a channel selective for K+, conductive to Cs+ and dependent on Ca2+.

Acetylcholine↗

PubMed1994

A nicotinic-like receptor mediates suppression of distortion product otoacoustic emissions by contralateral sound.

The purpose of this investigation was to provide in vivo pharmacologic characterization of a cholinergic receptor mediating the suppressive effects of medial olivocochlear (MOC) efferent activation. MOC neurons were activated by contralateral sound and the resulting suppression of ipsilateral distortion product otoacoustic emissions (DPOAEs) was monitored before and after intracochlear perfusions of cholinergic antagonists. Results revealed a dose-dependent blockade of contralateral suppression of DPOAEs by a wide variety of nicotinic and muscarinic cholinergic receptor antagonists, as well as by non-traditional antagonists of cholinergic activity. The nicotinic antagonists, alpha-bungarotoxin, curare and kappa-bungarotoxin, and the glycine antagonist, strychnine, blocked contralateral suppression at nanomolar concentrations and demonstrated similar potencies. IC50 values were 2.38 x 10(-7), 2.79 x 10(-7), 3.81 x 10(-7) and 2.96 x 10(-7) M, respectively. These agents were followed in potency by the nicotinic antagonist, trimethaphan (1.75 x 10(-6) M), the M3 muscarinic antagonist, 4-DAMP (1.88 x 10(-6) M) and the GABAA antagonist, bicuculline (2.39 x 10(-6) M). Increasingly greater concentrations of the muscarinic antagonists, atropine (9.52 x 10(-6) M), AF-DX 116 (2.72 x 10(-5) M) and pirenzepine (8.24 x 10(-4) M) were necessary to block contralateral suppression of DPOAEs. The in vivo pharmacology of this putative outer hair cell cholinergic receptor suggests that it may be a member of the nicotinic family of receptors.

Acoustic Stimulation↗

PubMed1994

In vitro pharmacologic characterization of a cholinergic receptor on outer hair cells.

Acetylcholine (ACh) is the major neurotransmitter released from the efferent fibers in the cochlea onto the outer hair cells (OHCs). The type of ACh receptor on OHCs and the events subsequent to receptor activation are unclear. Therefore we studied the effect of agonists and antagonists of the ACh receptor on isolated OHCs from the guinea pig. OHCs were recorded from in whole cell voltage and current clamp configuration. ACh induced an increase in outward K+ current (IACh) which hyperpolarized the OHCs. No desensitization to ACh application was observed. Cs+ replaced K+ in carrying the IACh. The IACh is Ca(2+)-dependent, time and voltage sensitive, and different from the IKCa induced by depolarization of the membrane potential. When tested at 100 microM, several agonists also induced outward current responses (acetylcholine > suberyldicholine > or = carbachol > DMPP) whereas nicotine, cytisine and muscarine did not. The IACh response to 10 microM ACh was blocked by low concentrations of traditional and non-traditional-nicotinic antagonists (strychnine > curare > bicuculline > alpha-bungarotoxin > thimethaphan) and by higher concentrations of muscarinic antagonists (atropine > 4-DAMP > AF-DX 116 > pirenzepine). Pharmacologically, the ACh receptor on OHCs is nicotinic.

Acetylcholine↗

PubMed1993

Contralateral sound suppresses distortion product otoacoustic emissions through cholinergic mechanisms.

Presentation of an acoustic signal to one ear can suppress sound-evoked activity recorded at the opposite ear. The suppression appears to be mediated by medial olivocochlear (MOC) efferent neurons synapsing with outer hair cells (OHCs) and acting through the MOC neurotransmitter, acetylcholine (ACh). The purpose of the present investigation was to study the suppression of distortion product otoacoustic emissions (DPOAEs) by contralateral sound and to examine whether the suppression could be blocked by known antagonists of olivocochlear (OC) efferent activity. Urethane-anesthetized guinea pigs were used. Perilymph spaces of ipsilateral cochleae were alternately perfused with artificial perilymph and drugs at 2.5 microliters/min for 10 min. After each period of perfusion, DPOAEs were measured before, during and after contralateral wideband noise (WBN) stimulation. Pre-perfusion, contralateral WBN attenuated the ipsilateral DPOAEs between 1-3 dB. This suppression was blocked reversibly by strychnine (10 microM), curare (10 microM) and atropine (20 microM), known antagonists of OC efferent activity. These results confirm the findings of Puel and Rebillard (1990) that contralateral WBN can suppress DPOAEs in anesthetized guinea pigs. Furthermore, results suggest that this efferent control of the cochlear mechanical response can either be mediated by both nicotinic and muscarinic cholinergic receptors, or that a single receptor with as yet undescribed structure and pharmacology mediates effects seen.

Acoustic Stimulation↗

PubMed1993

Volume regulation in cochlear outer hair cells.

Many cells placed in a hypotonic medium initially swell and then rapidly undergo a regulatory volume decrease (RVD) to return towards original volume. Re-exposure to the isotonic solution results in the cells shrinking followed by a regulatory volume increase (RVI). Previous studies have shown that isolated outer hair cells (OHCs) placed in a hypotonic medium swell and maintain this shape until returned to the original medium. We re-examined this apparent lack of cell volume regulation in OHCs. OHCs were isolated from guinea pig cochleae, mechanically dissociated and dispersed, and placed in a Hank's balanced salt solution (HBS). In the cells studied, switching the perfusate to a hypotonic HBS (290-280 mmol/kg) for 15 min resulted in an immediate shortening of the OHCs (i.e., volume increase). In 26% of the cells, this increase was followed by a return to original length during the time the cell was perfused with the hypotonic medium, a RVD. Twelve percent of the cells demonstrating a RVD also displayed a RVI. Omitting collagenase and increasing Ca2+ concentration did not increase the percentage of cells displaying a RVD, while gadolinium (Gd3+, 10 microM) decreased the percentage to zero. This is the first report of isolated OHCs undergoing cell volume regulation.

Animals↗

PubMed1992

Lowering extracellular chloride concentration alters outer hair cell shape.

In general, increasing external K+ concentration, as well as exposure to hypotonic medium, induces a shortening of outer hair cells (OHCs) accompanied by an increase in width and volume. One possible mechanism suggested for these changes is a movement of Cl- and/or water across the cell membrane. We therefore examined the role of Cl- in OHC volume maintenance by testing the effect of decreasing extracellular Cl- concentration on OHC length and shape. In addition, the effect of hypotonic medium was examined. OHCs were isolated from guinea pig cochleae, mechanically dissociated and dispersed, and placed in a modified Hanks balanced salt solution (HBS). Exposing the cells to a Cl(-)-free HBS produced an initial shortening, which was rapidly followed by an increase in length. After about 9 min of exposure to Cl(-)-free HBS, the cells appeared to lose all water and collapsed. Upon return to normal HBS, the OHCs returned to their normal shape. We speculate that the collapse of the OHCs may be due to the loss of intracellular Cl-, which, in turn, resulted in the loss of intracellular K+ and water. The results indicate that Cl- contributes greatly to the maintenance of OHC volume. In addition, we confirmed that isolated OHCs swell in hypotonic medium and maintain their swollen state until returned to normal medium. The mechanism for maintenance of the swollen state is unknown.

Animals↗