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The tectorial membrane & Dr Lionel Naftalin

Dear all

I have been talking to Dr Lionel Naftalin, (and to Dr Eve Lutz, who has been assisting him) who, though 94, is still involved in research. There is a particular part of his research that we feel should be continued. Unfortunately, he is not able to continue it himself, and the group with whom he is associated (namely the Strathclyde Institute of Pharmacy & Biomedical Sciences, Glasgow, Scotland) is not working in this area (and I’m really a computer modeler, without access to what would be required).

Here is my précis of the piece of work that I think needs done. Apologies for the incompleteness, and for the length of it. Further information may be found by contacting Dr Eve Lutz, dfs99109@xxxxxxxxxxxx : there is some further written material.

Early models of the cochlea (going back to Helmholtz and von Bekesy) considered that the basilar membrane was a resonator which had a maximal displacement at some point along its length in response to input to the cochlea, enabling spectral analysis of the incoming sound signal. Later work identified the inner hair cell as the transducer, with outer hair cells being an element of some form of amplifier and/ or damper. Both hair cell types are (essentially) attached at base to the basilar membrane, but have their hair tips attached to the tectorial membrane. Generally, the stereocilia on the IHC are considered as mechanoreceptors, and their movement opens K+ channels in the IHC which then result in changes at the base of the IHC causing spiking on the type 1 fibers of the auditory nerve. These K+ channels have been investigated in guinea pig [1], and they do seem to be fast enough to be suitable candidates. Further, the endolymph is very high in K+ concentration (157mM), and appears to be kept at a relatively large voltage which appears to be polarized across the tectorial membrane [2] This means (I believe) that there is likely to be some K+ passing through the ion channels even in the absence of any incoming sound, and this is backed up by the existence of spontaneous firing in some type 1 auditory nerve fibers.

None of this is new: the traditional wisdom suggests that it is the relative movement of the tectorial membrane and the basilar membrane which moves the stereocilia, thus modulating the K+ ion flow, and hence resulting in spikes being generated. But Naftalin [3, 4] points out that the energy in the sound signal is not sufficient to cause movement beyond small numbers of nanometers (and this is repeated by Ashmore [5]). Though not impossible, it is difficult to imagine that such small movements would be detectable reliably (and rapidly) in terms of the modulation of the K+ mechanoreceptor currents.

In the mean time there has been considerable interest in the functional qualities and microanatomy of the tectorial membrane: the material properties have been investigated both in the static case [6] and dynamically [7]; travelling waves in it have been analysed [8], as has its detailed mechanical properties [9]. What Naftalin is suggesting is that it is the particular characteristics of the colloidal gel that is the tectorial membrane that enables it to cause electrical changes as a result of minute acoustic perturbations. These electrical changes (rather than mechanical movements) are responsible for the modulation of the K+ influx at very low sound levels. This is alluded to in his paper [10]. In addition Naftalin has performed some initial experiments using an artificial gel membrane constructed from galactomannan, borax, and gelatin. Initial experiments by Naftalin suggest that when such a structure is prepared appropriately, and has a DC bias placed across it, it organizes into a set of regular dipoles (see http://www.cs.stir.ac.uk/~lss/undocumented/Fig3.tif), and that a small acoustic signal applied to this can result in an AC voltage being generated across the membrane, modulating the DC bias across the membrane. This, Naftalin suggests might be (i) the source of the cochlear microphonic, and (ii) the method whereby the K+ ion channel currents are modulated by small signals.

Although some very basic experiments have been performed, there is not enough data for publication: what we are interested in is getting someone to carry forward this work. The precise details of the preparation used are available (from Dr Eve Lutz), and she would able to supply further information from the earlier work done (but not published) by Dr Naftalin.

[1] T. Kimitsuki et al,  Hearing Research, 180 (2003) 85-90

[2] P. Wangemann, J. Physiol 576.1(2006) 11-21

[3] L. Naftalin, Physiol Chem and Physics 9 (1977) 337- 381

[4] L. Naftalin, Hearing Research 5 (1981) 307-315

[5]  J. F. Ashmore Experimental Physiology 79 (1994) 113-134

[6] D. M. Freeman et al Hearing Research 180 (2003) 11-27

[7] D. M Freeman et al Hearing Research 180 (2003) 1-10

[8] R. Ghaffari et al PNAS 104 (42) (Oct 16 2007)  16510-16515

[9] N. Gavara, R. S Chadwick PLOS one 4(3) (2009) e4877

[10] L. Naftalin and M. Mattey, Proceedings of the Conference on Nonlinear Coherent Structures in Physics and Biology, Heriot-Watt University, Edinburgh, July 95: http://www.ma.hw.ac.uk/solitons/procs/naftalin/naft.html

Professor Leslie S. Smith,

Head, Dept of Computing Science and Mathematics,
University of Stirling,
Stirling FK9 4LA, Scotland
Tel (44) 1786 467435 Fax (44) 1786 464551
www http://www.cs.stir.ac.uk/~lss/

Academic Excellence at the Heart of Scotland.
The University of Stirling is a charity registered in Scotland, number SC 011159.