The tectorial membrane & Dr Lionel Naftalin

[Leslie Smith <l.s.smith@xxxxxxxxxxxxx>]

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
l.s.smith@xxxxxxxxxxxxx
Tel (44) 1786 467435 Fax (44) 1786 464551
www http://www.cs.stir.ac.uk/~lss/






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