Biomedical subjects

G D Housley

Publications and source records attributed to G D Housley.

At least 19 recordsLinked to original sources

PubMed2006

Hair cells--beyond the transducer.

OVERVIEW: This review considers the "tween twixt and twain" of hair cell physiology, specifically the signaling elements and membrane conductances which underpin forward and reverse transduction at the input stage of hair cell function and neurotransmitter release at the output stage. Other sections of this review series outline the advances which have been made in understanding the molecular physiology of mechanoelectrical transduction and outer hair cell electromotility. Here we outline the contributions of a considerable array of ion channels and receptor signaling pathways that define the biophysical status of the sensory hair cells, contributing to hair cell development and subsequently defining the operational condition of the hair cells across the broad dynamic range of physiological function.

Animals↗

PubMed2005

Differential expression of ryanodine receptors in the rat cochlea.

This study examined the localization and functional expression of ryanodine receptors (RyR) within the cochlea using a combination of reverse transcription-polymerase chain reaction, immunolabeling techniques, and confocal Ca2+ imaging. All three RyR isoform mRNA transcripts were detected in the adult rat cochlea. Immunoperoxidase and immunofluorescence labeling showed that the three isoforms were differentially expressed. The most pronounced RyR protein expression, involving all three isoforms, occurred in the cell bodies of the spiral ganglion neurons. RyR3 labeling extended to the synaptic terminals innervating the inner and outer hair cells. RyR2 expression also occurred in the inner hair cells and supporting cells of the organ of Corti, while cells associated with ion homeostasis in the cochlea, such as the interdental cells of the spiral limbus (RyR1), and the epithelial cells of the spiral prominence and basal cells of the stria vascularis (RyR2 and RyR3), were also immunopositive. The functionality of RyR-gated Ca2+ stores in the spiral ganglion neurons was shown by confocal calcium imaging of fluo-4 fluorescence in rat cochlear slices. Caffeine (5 mM) evoked an increase in intracellular Ca2+ concentration in the cell bodies of the spiral ganglion neurons which occurred inthe absence of external Ca2+. Ryanodine (50 nm-1 microM) evoked comparable increases in intracellular Ca2+ concentration. These findings suggest that RyR-mediated Ca2+ release may be involved in auditory neurotransmission, sound transduction, and cochlear electrochemical homeostasis.

Animals↗

PubMed2004

P2 receptors modulate respiratory rhythm but do not contribute to central CO2 sensitivity in vitro.

Multiple brainstem sites are proposed to contribute to central respiratory chemosensitivity, however, the underlying molecular mechanisms remain unknown. P2X2 subunit-containing ATP receptors, which mediate pH-sensitive currents, appear to contribute to central chemosensitivity in vivo [J. Physiol. 523 (2000) 441]. However, recent data from P2X2 knockout mice [J. Neurosci. 23 (2003) 11315] indicate that they are not essential. To further explore the role of P2 receptors in central chemosensitivity, we examined the effects of P2 receptor agonists/antagonists on respiratory-related activity and CO2-sensitivity of rhythmically-active in vitro preparations from neonatal rat. Our main findings: (i) that putative chemosensitive regions of the ventrolateral medulla are immunoreactive for the P2X2 subunit; (ii) that ATP potentiates respiratory frequency in a dose-dependent, and PPADS-sensitive (P2 receptor antagonist), manner; and (iii) that the increase in burst frequency produced by increasing CO2 is unaffected by PPADS, indicate that ATP is a potent modulator of respiratory activity, but that P2 receptors do not contribute to central chemosensitivity in vitro.

Action Potentials↗

PubMed2004

Noise exposure induces up-regulation of ecto-nucleoside triphosphate diphosphohydrolases 1 and 2 in rat cochlea.

Extracellular ATP acting via P2 receptors in the inner ear initiates a variety of signaling pathways that may be involved in noise-induced cochlear injury. Nucleoside triphosphate diphosphohydrolase (NTPDase)1/CD39 and NTPDase2/CD39L1 are key elements for regulation of extracellular nucleotide concentrations and P2 receptor signaling in the cochlea. This study characterized the effect of noise exposure on regulation of NTPDase1 and NTPDase2 expression in the cochlea using a combination of real-time RT-PCR, immunohistochemistry and functional studies. Adult Wistar rats were exposed to broad band noise at 90 dB and 110 dB sound pressure level (SPL) for 72 h. Exposure to 90 dB SPL induced a small and temporary change of auditory thresholds (temporary threshold shift), while exposure to 110 dB SPL induced a robust and permanent change of auditory thresholds (permanent threshold shift). NTPDase1 and NTPDase2 mRNA transcripts were upregulated in the cochlea exposed to 110 dB SPL, while mild noise (90 dB SPL) altered only NTPDase1 mRNA expression levels. Changes in NTPDases expression did not correlate with levels of circulating corticosterone, implying that the up-regulation of NTPDases expression was not stress-related. Semi-quantitative immunohistochemistry in the cochlea exposed to 110 dB SPL localized the increased NTPDase1 and NTPDase2 immunostaining in the stria vascularis and up-regulation of NTPDase2 in the intraganglionic spiral bundle. In contrast, NTPDase1 was down-regulated in the cell bodies of the spiral ganglion neurones. Distribution of NTPDases was not altered in the cochlea exposed to 90 dB SPL. Functional studies revealed increased ectonucleotidase activities in the cochlea after exposure to 110 dB SPL, consistent with up-regulation of NTPDases. The changes in NTPDases expression may reflect adaptive response of cochlear tissues to limit ATP signaling during noise exposure.

Acoustic Stimulation↗

PubMed2002

ATP-gated currents in rat primary auditory neurones in situ arise from a heteromultimetric P2X receptor subunit assembly.

Spiral ganglion neurones provide the primary afferent innervation to sensory hair cells within the mammalian cochlea. Recent evidence suggests that their function may be modulated by purinergic signalling mechanisms, associated with release of adenosine 5'-triphosphate (ATP). Utilising a newly developed slice preparation of the neonatal rat cochlea, we have investigated the response of neurones in situ, to purinergic agonists and antagonists using whole-cell voltage clamp recordings. In cells identified as type I spiral ganglion neurones on the basis of morphology and voltage-dependent conductances, pressure-applied ATP, alpha,beta-methyleneATP (alpha,beta-meATP), 2-methylthioATP (2-MeSATP) and adenosine 5'-diphosphate (ADP) elicited a consistent phenotype of desensitising, inwardly rectifying current. The ATP-activated currents were reversibly blocked by the P2X receptor antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 microM), and 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP; IC(50) 407 nM). Neurones were more sensitive to ATP at low pH. The EC(50) value for ATP shifted from 18 microM at pH 7.3, to 1 microM at pH 6.3, with Hill coefficients of approximately 1. The results indicate that ATP-gated ion channels in spiral ganglion neurones arise from a specific heteromultimeric assembly of P2X receptor subunits which has no correspondence with present recombinant P2X receptor models.

Adenosine Triphosphate↗

PubMed2002

A-type potassium currents dominate repolarisation of neonatal rat primary auditory neurones in situ.

Spiral ganglion neurones provide the afferent innervation to cochlear hair cells. Little is known of the molecular physiological processes associated with the differentiation of these neurones, which occurs up to and beyond hearing onset. We have identified novel A-type (inactivating) potassium currents in neonatal rat spiral ganglion neurones in situ, which have not previously been reported from the mammalian cochlea, presumably as a consequence of altered protein expression associated with other preparations. Under whole-cell voltage clamp, voltage steps activated both A-type and non-inactivating outward currents from around -55 mV. The amplitude of the A-type currents was dependent on the holding potential, with steady-state inactivation relieved at hyperpolarised potentials. At -60 mV (close to the resting potential in situ) the currents were approximately 30% enabled. The inactivation kinetics and the degree of inactivation varied between cells, suggesting heterogeneous expression of multiple inactivating currents. A-type currents provided around 60% of total conductance activated by depolarising voltage steps from the resting potential, and were very sensitive to bath-applied 4-aminopyridine (0.01-1 mM). Tetraethylammonium (0.1-30 mM) also blocked the majority of the A-type currents, and the non-inactivating outward current, but left residual fast inactivating A-type current. Under current clamp, neurones fired single tetrodotoxin-sensitive action potentials. 4-Aminopyridine relieved the A-type current mediated stabilisation of membrane potential, resulting in periodic small amplitude action potentials. This study provides the first electrophysiological evidence for A-type potassium currents in neonatal spiral ganglion neurones and shows that these currents play an integral role in primary auditory neurone firing.

Action Potentials↗

PubMed2001

Transient expression of P2X(1) receptor subunits of ATP-gated ion channels in the developing rat cochlea.

The expression pattern of the ATP-gated ion channel P2X(1) receptor subunit was studied in the developing rat cochlea by riboprobe in situ hybridisation and immunohistochemistry. Embryonic (E12, E14, E16 and E18) and postnatal (P0, P2, P4, P6, P10 and adult) rat cochleae were examined. Both mRNA and protein localisation techniques demonstrated comparable P2X(1) receptor expression from E16 until P6 but this expression was absent at later developmental stages. P2X(1) receptor mRNA expression was localised within the otic capsule and associated mesenchyme (from E16 to P6), spiral limbus (from P0 to P6) and within the spiral ligament adjacent to the insertion of Reissner's membrane (from P2 to P6). P2X(1) receptor protein had a similar distribution based upon immunoperoxidase localisation. P2X(1) receptor-like immunoreactivity was detected in the otic capsule and the surrounding mesenchyme (from E16 to P6), spiral limbus (from P0) and epithelial cells of Reissner's membrane (from P2 to P6). The spiral ganglion neurones showed the earliest P2X(1) receptor expression (from E16 to P6). This became associated with immunolabelling of their afferent neurite projections to the base of the developing inner and outer hair cells (observed from E18 and peaking at P2). Immunolabelling of the efferent nerve fibres of the intraganglionic spiral bundle (from E18 to P6) within the spiral ganglion was also observed. The results suggest that ATP-gated ion channels assembled from P2X(1) receptor subunits provide a signal transduction pathway for development of afferent and efferent innervation of the sensory hair cells and purinergic influence on cochlear morphogenesis.

Adenosine Triphosphate↗

PubMed2001

Positional analysis of guinea pig inner hair cell membrane conductances: implications for regulation of the membrane filter.

In mammals, sound transduction by inner hair cells (IHC) generates a receptor potential whose amplitude and phase drive auditory nerve firing. The membrane filter properties that define the input-output function of IHC are derived from membrane conductance and capacitance. These elements of the membrane filter were quantified using whole-cell voltage clamp of IHC from the four turns of the guinea pig cochlea. IHC membrane properties were remarkably constant along the cochlea, in contrast with all other auditory hair cell systems, and suggests that extrinsic processes such as the active filter provided by the outer hair cells are matched to a constant transfer function of the IHC. Two outwardly rectifying K+ currents contribute to the IHC membrane conductance. These combined currents activate at approximately -55 mV. IHC mean input resistance was 140 M ohm and capacitance was 10.0 pF, generating a membrane time constant of 1.4 ms or a corner frequency of approximately 115 Hz, which is consistent with reported low-frequency roll-off of the IHC AC receptor potential in vivo. Approximately 40% of the 313-1 nS total K+ conductance about 0 mV was attributed to charybdotoxin-sensitive K(Ca) channels (also sensitive to cell dialysis with the Ca2+ chelator BAPTA or removal of extracellular Ca2+). The only known ligand-activated conductance in mature IHC, the P2X receptor conductance, averaged 31 nS (activated by 400 microM ATP; about -75 mV) irrespective of cell origin. Thus, regulation of intracellular Ca2+ and activation of P2X receptors by extracellular ATP provide capacity for local dynamic fine-tuning of the IHC membrane filter.

Animals↗

PubMed2000

A technique for slicing the rat cochlea around the onset of hearing.

The cochlea presents a considerable challenge to the study of sound transduction and auditory neurotransmission. This arises from the location of the sensory, supporting and secretory epithelia, and primary auditory neurons within a complex ossified spiral structure comprised of three separate fluid-filled chambers. We have developed a novel cochlear slice preparation, which provides access to the highly differentiated tissues while retaining structural integrity and cell viability. Our technique for slicing the cochlea and imaging tissue structure facilitates the study of peripheral auditory signaling in situ. The preparation was developed in the neonatal rat (postnatal days 4-14) and is based on the use of vibrating blade microtome slicing after perfusing the perilymphatic compartments with chilled Pluronic F127 NF, a block copolymer gel. This material is liquid when cold, and sets when warmed to room temperature, stabilizing the cochlear fluid-filled compartments and thereby supporting the cochlear partition during slicing. Slices (150-300 microm) of neonatal rat cochlea, imaged using infrared videomicroscopy, allow tight-seal voltage clamp recordings from a variety of cell types. Recordings obtained from primary auditory neurons, hair cells, supporting cells, and Reissner's membrane epithelial cells verify the viability of the tissues in the preparation. Data includes novel evidence for glutamatergic and purinergic co-transmission by primary auditory neurons. The preparation has considerable potential in a range of molecular physiological applications requiring cell-specific targeting with retention of cell connectivity.

Animals↗

PubMed2000

P2X2 receptor expression by interstitial cells of Cajal in vas deferens implicated in semen emission.

Male reproduction is dependent upon seminal emission mediated by vas deferens contraction. This drives spermatic fluid to the prostatic urethra during ejaculation. We localize interstitial cells of Cajal (ICC), which express P2X2 receptor, subunits of ATP-gated ion channels, to rat, mouse and guinea-pig vas deferens submucosa. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of rat vas deferens resolved two functional splice variant transcripts of the P2X2 receptor subunit. The P2X2 receptor mRNA was localized principally within the lamina propria (submucosal) region of the rat vas deferens using in situ hybridization (ISH) and in situ RT-PCR-ISH. Immunohistochemistry using rat, mouse and guinea-pig vas deferens tissues confirmed expression of P2X2 receptor protein within the lamina propria, particularly within a dense column of small spindle-shaped cells adjacent to the columnar epithelial cells which line the lumen. This immunoreactivity was co-localized with neurone-specific enolase (NSE) and c-Kit protein expression, gene markers for ICC. Mucosal mast cells were distinguished from ICC by toluidine blue staining. Choline acetyltransferase immunoreactivity, a marker for post-ganglionic parasympathetic innervation, occurred on the lateral margin of the lamina propria and extended into the inner longitudinal muscle layer. P2X1 receptor immunolabelling was associated with sympathetic innervation of the smooth muscle in the outer longitudinal and circular muscle layers, but not the inner longitudinal layer. The physiological significance of the vas deferens ICC which express P2X2 receptors remains to be established. Possible roles include regulation of smooth muscle activity or mucosal secretion utilizing local ATP signaling, both of which would affect semen transport.

Acridine Orange↗

PubMed2000

Purinergic signalling: an experimental perspective.

Investigation of the multiple roles of extracellular nucleotides in the cochlea has developed from analysis of ATP-activated conductances in single sensory hair cells. Molecular probes such as radiolabelled ATP analogues and radiolabelled mRNA for ATP-gated ion channel subunits (P2X receptors) rapidly revealed the extensive nature of ATP signalling in this sensory organ. This has provided a foundation for physiological investigations which put extracellular nucleotides at the centre of homeostatic regulation of the driving force for sound transduction, modulation of mechanical tuning, control of cochlear blood flow and auditory neurotransmission. The purinergic signal transduction pathways associated with these processes have several novel features of significance to the broader field of purinergic neuroscience. In turn, these studies have benefited from the recent experimental advances in the field of purinergic signalling, a significant component of which is associated with the work of Professor Geoffrey Burnstock.

Adenosine Triphosphate↗

PubMed2000

Immunohistochemical localization of adenosine 5'-triphosphate-gated ion channel P2X(2) receptor subunits in adult and developing rat cochlea.

Substantial in vitro and in vivo data support a role for extracellular adenosine 5;-triphosphate (ATP) and associated P2 receptors in cochlear function. However, the precise spatiotemporal distribution of the involved receptor protein(s) has not been determined. By using a specific antiserum and immunoperoxidase labeling, the tissue distribution of the P2X(2) subunit of the ATP-gated ion channel was investigated. Here, we describe the first extensive immunohistochemical mapping of P2X(2) receptor subunits in the adult and developing rat cochlea. In the adult, immunoreactivity was observed in most cells bordering on the endolymphatic compartment (scala media), particularly in the supporting cells. Hair cells were not immunostained by the P2X(2) antiserum, except for outer hair cell stereocilia. In addition, weak immunolabeling was observed in some spiral ganglion neurons. P2X(2) receptor subunit protein expression during labyrinthine ontogeny was detected first on embryonic day 19 in the spiral ganglion and in associated nerve fibers extending to the inner hair cells. Immunostaining also was observed underneath outer hair cells, and, by postnatal day 6 (P6), intense immunolabeling was seen in the synaptic regions of both types of hair cell. Supporting cells of the sensory epithelium were labeled at P0. This labeling became most prominent from the onset of cochlear function (P8-P12). Conversely, expression in the vascular stria declined from this time. By P21, the pattern of immunolabeling was similar to that found in the adult. The localization and timing of P2X(2) immunoreactivity suggest involvement of extracellular ATP and associated ATP-gated ion channels in important physiological events, such as inner ear ontogeny, sound transduction, cochlear micromechanics, electrochemical homeostasis, and auditory neurotransmission.

Adenosine Triphosphate↗

PubMed2000

Physiological effects of extracellular nucleotides in the inner ear.

1. Electrochemical homeostasis, sound transduction and auditory neurotransmission in the cochlea are influenced by extracellular purines and pyrimidines. 2. Evidence that ATP and related nucleotides influence inner ear function arises from a considerable number of cellular, molecular and physiological studies in vitro and in vivo. 3. With a full understanding of these processes, which include ionotropic (P2X receptor) and metabotropic (P2Y receptor) signal transduction pathways, signal termination involving ecto-nucleotidases and recycling via nucleoside transporters, exciting possibilities emerge for treating hearing disorders, such as Meniere's disease, tinnitus and sensorineural deafness.

Adenosine Triphosphate↗

PubMed1999

Evidence for alternative splicing of ecto-ATPase associated with termination of purinergic transmission.

Ectonucleotidases provide the signal termination mechanism for purinergic transmission, including fast excitatory neurotransmission by ATP in the CNS. This study provides evidence for ectonucleotidase expression in the rat cochlea, brain and other tissues. In addition to detection of rat ecto-ATPase and ecto-ATPDase in these tissues, we identify a novel ecto-ATPase splice variant arising from the loss of a putative exon (193 bp) in the C-terminal coding region. This is the first evidence of alternative splicing in the ecto-ATPase gene family. Splicing of the 193-bp putative exon containing a stop codon extends the open reading frame and provides translation of an additional 50 amino acids compared with the isoform isolated earlier from the rat brain (rEATPase(A); GenBank accession #Y11835). The splice variant (rEATPase(B); GenBank accession #AF129103) encodes 545 amino acids with a predicted protein molecular mass of 60 kDa. rEATPase(B) contains a long cytoplasmic tail (62 amino acids) with three potential protein kinase CK2 phosphorylation sites not present in rEATPase(A). Co-expression of two ecto-ATPase isoforms with different regulatory sites suggests that the extracellular ATP signal levels may be differently influenced by intracellular feedback pathways.

Adenosine Triphosphatases↗

PubMed1999

Expression of the P2X(2) receptor subunit of the ATP-gated ion channel in the cochlea: implications for sound transduction and auditory neurotransmission.

Extracellular ATP has multimodal actions in the cochlea affecting hearing sensitivity. ATP-gated ion channels involved in this process were characterized in the guinea pig cochlea. Voltage-clamped hair cells exhibited a P2 receptor pharmacology compatible with the assembly of ATP-gated ion channels from P2X(2) receptor subunits. Reverse transcription-PCR experiments confirmed expression of the P2X(2-1) receptor subunit mRNA isoform in the sensory epithelium (organ of Corti); a splice variant that confers desensitization, P2X(2-2), was the predominant subunit isoform expressed by primary auditory neurons. Expression of the ATP-gated ion channel protein was localized using a P2X(2) receptor subunit-specific antiserum. The highest density of P2X(2) subunit-like immunoreactivity in the cochlea occurred on the hair cell stereocilia, which faces the endolymph. Tissues lining this compartment exhibited significant P2X(2) receptor subunit expression, with the exception of the stria vascularis. Expression of ATP-gated ion channels at these sites provides a pathway for the observed ATP-induced reduction in endocochlear potential and likely serves a protective role, decoupling the "cochlear amplifier" in response to stressors, such as noise and ischemia. Within the perilymphatic compartment, immunolabeling on Deiters' cells is compatible with purinergic modulation of cochlear micromechanics. P2X(2) receptor subunit expression was also detected in spiral ganglion primary afferent neurons, and immunoelectron microscopy localized these subunits to postsynaptic junctions at both inner and outer hair cells. The former supports a cotransmitter role for ATP in a subset of type I spiral ganglion neurons, and latter represents the first characterization of a receptor for a fast neurotransmitter associated with the type II spiral ganglion neurons.

Adenosine Triphosphate↗

PubMed1999

ATP-gated ion channel expression in primary auditory neurones.

Extracellular ATP acts via ionotropic P2X receptors to mediate fast neurotransmission in the central and autonomic nervous systems. Recent data, including identification of P2X2 receptor mRNA expression by spiral ganglion neurones, suggests that purinergic signalling may influence auditory neurotransmission via ATP-gated ion channels assembled from these subunits. Expression of the P2X2 receptor was localized to the region of the spiral ganglion neurone synapses with the inner hair cells using a P2X2 receptor specific antiserum. Whole-cell patch clamping of neurones cultured from post-natal day 3-5 spiral ganglia demonstrated a heterogeneity of ATP-activated conductances, consistent with the functional expression of P2X2 receptor subunit isoforms along with possible co-expression of additional P2X receptor subunits. These data provide substantive support for a purinergic transmission element at the peripheral auditory synapse.

Adenosine Triphosphate↗

PubMed1999

Distribution of the P2X2 receptor subunit of the ATP-gated ion channels in the rat central nervous system.

The distribution of the P2X2 receptor subunit of the adenosine 5'-triphosphate (ATP)-gated ion channels was examined in the adult rat central nervous system (CNS) by using P2X2 receptor-specific antisera and riboprobe-based in situ hybridisation. P2X2 receptor mRNA expression matched the P2X2 receptor protein localisation. An extensive expression pattern was observed, including: olfactory bulb, cerebral cortex, hippocampus, habenula, thalamic and subthalamic nuclei, caudate putamen, posteromedial amygdalo-hippocampal and amygdalo-cortical nuclei, substantia nigra pars compacta, ventromedial and arcuate hypothalamic nuclei, supraoptic nucleus, tuberomammillary nucleus, mesencephalic trigeminal nucleus, dorsal raphe, locus coeruleus, medial parabrachial nucleus, tegmental areas, pontine nuclei, red nucleus, lateral superior olive, cochlear nuclei, spinal trigeminal nuclei, cranial motor nuclei, ventrolateral medulla, area postrema, nucleus of solitary tract, and cerebellar cortex. In the spinal cord, P2X2 receptor expression was highest in the dorsal horn, with significant neuronal labeling in the ventral horn and intermediolateral cell column. The identification of extensive P2X2 receptor immunoreactivity and mRNA distribution within the CNS demonstrated here provides a basis for the P2X receptor antagonist pharmacology reported in electrophysiological studies. These data support the role for extracellular ATP acting as a fast neurotransmitter at pre- and postsynaptic sites in processes such as sensory transmission, sensory-motor integration, motor and autonomic control, and in neuronal phenomena such as long-term potentiation (LTP) and depression (LTD). Additionally, labelling of neuroglia and fibre tracts supports a diverse role for extracellular ATP in CNS homeostasis.

Adenosine Triphosphate↗

PubMed1999

P2X receptor-mediated changes in cochlear potentials arising from exogenous adenosine 5'-triphosphate in endolymph.

Our previous studies have determined the presence of adenosine 5'-triphosphate (ATP) in the cochlear fluids and shown that extracellular ATP introduced into the endolymphatic compartment of the guinea pig cochlea has a significant dose-dependent suppressive effect on both endocochlear potential (EP) and cochlear microphonic (CM), which is mediated via P2 receptors. In the present study, the influence of P2 receptor agonists and antagonists on this suppressive effect was investigated to characterise the subtypes of P2 receptor mediating the ATP-induced effect on cochlear function. Using a double-barreled pipette attached to a pressure injector, small volumes (2-10 nl) of ATP (0.01-1 mM) and P2 receptor agonists or P2 receptor antagonists in artificial endolymph were introduced into the scala media of the first (basal) and third turns of the guinea pig cochlea, while the EP and CM were monitored. ATP and P2 receptor agonists (5x10(-14)-1x10(-11)cibacron blue. Neither adenosine nor uridine 5'-triphosphate (2x10(-13)-2x10(-11) moles) nor the P2 receptor antagonists on their own had any effect on EP and CM. The ATP effect on the potentials was greater at the third cochlear turn when compared to the first turn. These results provide evidence that in the endolymphatic compartment of the guinea pig, the extracellular ATP effect on cochlear function is likely mediated through an interaction with P2 receptors which assemble as ATP-gated ion channels.

Adenosine Triphosphate↗