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Liam J Skinner

Publications and source records attributed to Liam J Skinner.

8 recordsLinked to original sources
PubMed2005

Ryanodine receptors and BK channels act as a presynaptic depressor of neurotransmission in cochlear inner hair cells.

Ryanodine receptors (RyRs) are known to contribute to the regulation of free cytosolic calcium concentration. This family of intracellular calcium channels plays a significant role in calcium-induced-calcium-release (CICR), and have been implicated in calcium-dependent processes requiring exquisite spatio-temporal regulation. In order to characterize the importance of these intracellular calcium channels in cochlear physiology, we perfused the guinea pig cochlea with antagonistic concentrations of ryanodine. The distortion products of the cochlear microphonic and the compound action potential of the auditory nerve were reversibly inhibited by ryanodine (IC(50)=27.3 microm, Hill coefficient=1.9), indicating an action at the cochlear amplifier. Single auditory nerve fibre recordings showed that ryanodine slightly increased spontaneous firing rates by 22%, suggesting an excitatory effect of ryanodine. This paradoxical effect could be explained by an inhibitory action of ryanodine on presynaptic BK channels of inner hair cells (IHC). Indeed, perfusing iberiotoxin also increased the spontaneous firing activity of the auditory nerve fibres. Furthermore, whole-cell patch-clamp recordings demonstrated that ryanodine inhibits BK currents at the IHC level. Conversely, immunohistochemistry demonstrated a strong expression of RyR in IHCs and, more particularly, below the cuticular plate where membranous BK channels are highly expressed. Overall, the study demonstrated a key role for RyR and CICR in signal transduction at the IHCs. We therefore propose that coupled RyR--BK channels act to suppress the fast neurotransmission in IHCs.

Action Potentials↗
PubMed2004

Detection of bone marrow micrometastases in the rib marrow of head and neck cancer patients: a prospective pilot study.

Flow cytometry has been validated as an objective method of demonstrating and quantifying micrometastases. Micrometastases within bone marrow indicate a poor prognosis in patients with upper gastrointestinal, colorectal and breast epithelial tumours. We prospectively sought to assess the feasibility of testing rib marrow for bone marrow micrometastases in head and neck cancer and to report their frequency in a cohort of patients. Nine patients were enrolled in the study. Bone marrow was obtained before manipulation of the primary tumour. Micrometastatic cells were detected by staining contaminant cytokeratin-18 positive cells and using the twin techniques of immuncytochemistry and flow cytometry. Cellular marrow was retrieved in 100% of cases. Micrometastases were detected in one out of nine epithelial tumours on both flow cytometry and immunocytochemistry. The detection rate appeared to be independent of TN staging. We were unable to culture the cells. Preoperative detection of bone marrow micrometastases may reflect transient shedding of cells, metastatic potential or residual disease. This prospective study confirms the feasibility of using rib marrow in future studies investigating micrometastases in head and neck cancer.

Adult↗
PubMed2004

Intracochlear perfusion of pneumolysin, a pneumococcal protein, rapidly abolishes auditory potentials in the Guinea pig cochlea.

OBJECTIVE: Bacterial meningitis and chronic suppurative otitis media caused by Streptococcus pneumoniae are associated with considerable otological morbidity. Specifically, sensorineural hearing loss is a permanent sequela in a third of those who contract pneumococcal meningitis. Pneumolysin, a pneumococcal protein, has been implicated as one of the main virulence/cytotoxic factors. Its pathogenicity is intimately dependent on an ability to form transmembrane pores on binding with cholesterol in target tissues. MATERIAL AND METHODS: We perfused wild-type pneumolysin, at a number of different concentrations, into the guinea pig cochlea and used electrocochleography to characterize the effects of this cytolytic exotoxin in the organ of Corti. RESULTS: Intracochlear perfusion of pneumolysin (10 microg/50 microl) reduced the compound action potential of the auditory nerve within seconds. The cochlear microphonics (f1=8 kHz, f2=9.68 kHz) and their distortion product (2f1-f2) were also reduced, albeit in a slightly less dramatic fashion. At lower concentrations (1 microg/50 microl), a selective and earlier effect on inner hair cells was observed. CONCLUSIONS: These results clearly show that significant ototoxicity ensues when sensory cells of the organ of Corti are exposed to pneumolysin (and complete cochlear death when the concentration is high enough). Toxicity is dose-dependent and appears to be site-sensitive. This may have implications for any possible future protective strategies against pneumococcal disease in the ear.

Acoustic Stimulation↗
PubMed2004

Argon plasma coagulation in the treatment of tonsil remnants.

Tonsil remnants are a problematic outcome in a subset of patients undergoing tonsillectomy. Treatment options are rarely discussed in the literature. This is the first description of the use of argon plasma coagulation (APC) in this setting. APC is based on the principle of ionised argon gas creating a conductive plasma between an activating electrode and a tissue surface. We describe the usability and clinical efficacy of this modality in a group of six patients.

Adolescent↗
PubMed2003

Contribution of BK Ca2+-activated K+ channels to auditory neurotransmission in the Guinea pig cochlea.

Large-conductance calcium-activated potassium (BK) channels are known to play a prominent role in the hair cell function of lower vertebrates where these channels determine electrical tuning and regulation of neurotransmitter release. Very little is known, by contrast, about the role of BK channels in the mammalian cochlea. In the current study, we perfused specific toxins in the guinea pig cochlea to characterize the role of BK channels in cochlear neurotransmission. Intracochlear perfusion of charybdotoxin (ChTX) or iberiotoxin (IbTX) reversibly reduced the compound action potential (CAP) of the auditory nerve within minutes. The cochlear microphonics (CM at f1 = 8 kHz and f2 = 9.68 kHz) and their distortion product (DPCM at 2f1-f2) were essentially not affected, suggesting that the BK specific toxins do not alter the active cochlear amplification at the outer hair cells (OHCs). We also tested the effects of these toxins on the whole cell voltage-dependent membrane current of isolated guinea pig inner hair cells (IHCs). ChTX and IbTX reversibly reduced a fast outward current (activating above -40 mV, peaking at 0 mV with a mean activation time constant tau ranging between 0.5 and 1 ms). A similar block of a fast outward current was also observed with the extracellular application of barium ions, which we believe permeate through Ca2+ channels and block BK channels. In situ hybridization of Slo antisense riboprobes and immunocytochemistry demonstrated a strong expression of BK channels in IHCs and spiral ganglion and to a lesser extent in OHCs. Overall, our results clearly revealed the importance of BK channels in mammalian cochlear neurotransmission and demonstrated that at the presynaptic level, fast BK channels are a significant component of the repolarizing current of IHCs.

Acoustic Stimulation↗
PubMed2003

Randomized controlled trial comparing argon plasma coagulation tonsillectomy with conventional techniques.

Argon plasma coagulation (APC) is based on the principle of ionized argon creating a conductive plasma between an activating electrode and a tissue surface. To date, its use in tonsillectomy has not been extensively examined. The purpose of this randomized controlled trial was to assess the clinical efficacy of APC as a tool for this common surgical procedure. Forty patients were randomized into two groups--treatment A (conventional tonsillectomy, n = 20) and treatment B (APC tonsillectomy, n = 20). Trial end-points included a) operative time, b) intra-operative blood loss, and c) objective assessment of post-operative pain, by completion of a visual analogue pain score chart, over a two-week period. Thirty-one patients were available for analysis. There was a statistically significant reduction in the intra-operative blood loss with treatment B (p = 0.02). There was no statistical difference between both groups for the other outcome measures. First clinical experience with this treatment modality shows that it is an attractive alternative to conventional tonsillectomy and may offer possible benefits.

Adolescent↗
PubMed2002

Complete vascular ring detected by barium esophagography.

The diagnosis of a vascular ring can be made on the basis of characteristic findings on barium esophagography. We report a case of a double aortic arch in a 9-month-old girl that was diagnosed in this manner, and we briefly review the anatomic characteristics of vascular rings.

Aorta, Thoracic↗