Address for correspondence: Manning J. Correia, Ph.D., Room 7.102, Blocker Medical Research Building, UTMB, Galveston, Texas 77555-1063, USA. Voice: (409) 772-2708; fax: (409) 772-2694.
correia{at}enterprise.utmb.edu
Recent electrophysiological studies in pigeon have demonstrated
that potassium channels are completely functional in regenerated
type II hair cells at 21 days post-treatment (PT) with ototoxic
doses of streptomycin. The currents return in the order they
appear during development. The mixture of ionic currents in
a regenerated type II hair cell in a particular region of the
neuroepithelium is the same as in its ancestor in that region.
The return of currents in regenerated type I hair cells is more
complicated. The dominant conductance g
KI is not present until
after 70 days PT. Before 70 days, the ionic currents in type
I hair cells resemble those of regenerated type II hair cells,
suggesting that the ionic currents in type II hair cells might
be precursors of the ionic currents in regenerated type I hair
cells. New data show that at one year PT, the kinetics and drug
sensitivity of the dominant K
+ conductance in type I hair cells
are identical to g
KI. Supporting cells, believed to be the precursors
of regenerated type II hair cells, have effectively no voltage-gated
outward potassium channels, suggesting that regenerated type
II hair cells must develop these channels
de novo. The next
step is to understand the mechanisms by which the potassium
channel protein is synthesized, migrates through the cytosol,
and is inserted into the plasmalemma of regenerating hair cells.
These mechanisms are unknown. We propose that intracellular
calcium is involved in this process, as well as in the differentiation,
proliferation, and gene regulation of precursor cells fated
to become hair cells.
