Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, C15

Oral Communications

Zebrafish: an emerging model for investigating hair cell physiology and function

J. Olt1, S. Johnson1, W. Marcotti1

1. Biomedical Science, University of Sheffield, Sheffield, United Kingdom.

Hair cells convert sound information into neuronal activity with remarkable precision, fidelity and reliability in the inner ear and vestibular system. Although hair cells have been studied extensively in the last few decades, and we understand a great deal about their development and function in vitro, we still do not know how they operate in vivo. We used the zebrafish to investigate the biophysical properties and the development of the hair cells in vivo (1).Whole-cell patch clamp recordings were obtained from hair cells in the primary neuromast of the lateral line of larval (3.0-5.2 dpf; days post fertilisation) and juvenile (17-37 dpf) zebrafish (Danio rerio). Recordings were performed at room temperature or at the temperature where fish are kept (28 °C). Larvae were paralysed by an injection of 125 μM α-bungarotoxin into the heart and the blood flow and heart rate were constantly monitored. Juveniles were briefly anaesthetised with 0.04% MS-222 and then decapitated. Membrane currents and neurotransmitter release (measured as change in membrane capacitance) were investigated from lateral line hair cells. Values are given as mean ± SEM.Hair cells expressed different K+-currents: IK,D, IA, Ih, IK,Ca. The expression of those currents differed depending on the position within the neuromast (centre vs. edge) and with age (larvae vs. juvenile). Of the 41 larval hair cells investigated, 80% showed the following current profile: IK,D, IK,Ca and a very small IA. About 34% of hair cells expressed Ih and a large IA was only seen in 17 % of cells (n = 41). In the juvenile zebrafish, the size of the total outward K+ current in hair cells was found to be similar to that of larval cells (larvae: 335 ± 18 mV, n = 41, juvenile: 400 ± 30 mV, n = 24), indicating that the overall number of K+ channels is unlikely to increase with development. However, in juvenile zebrafish we found a larger proportion (about 53% compared to 17% in larvae) expressing the large A-type current. Furthermore, the A-type was almost exclusively expressed in hair cells positioned in the centre of the neuromast, which agrees with previous morphological observations indicating that they have a more mature phenotype compared to cells positioned at the edge of the sensory organ (2, 3).Hair cells in juvenile zebrafish also show measurable Ca2+ currents (-10.5 ± 2.7 pA at -30 mV, n = 6) and neurotransmitter release (6.6 ± 0.6 fF, n = 5), which reflects about 150 calcium channels and around 178 vesicles.This study provides crucial information on the development and function of sensory hair cells of the zebrafish in vivo. However, it is important to consider that the majority of hair cells only reach maturity from juvenile stages. Consequently, future in vivo studies will require a new approach for zebrafish older than 5.2 dpf.

Where applicable, experiments conform with Society ethical requirements