AJP - Cell Physiology, Vol 258, Issue 6 C1051-C1061, Copyright © 1990 by American Physiological Society
Olfactory neurons exhibit heterogeneity in depolarization-induced calcium changes
D. Restrepo and J. H. Teeter
Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104.
Olfactory neurons from the channel catfish, Ictalurus punctatus, were
isolated by a brief (15 min) treatment with papain. After incubation with
fura-2 acetoxymethyl ester (fura-2/AM) for 1 h, the isolated olfactory
receptor cells are found to hydrolyze fura-2/AM to fura-2 free acid without
detectable traces of intermediate products of hydrolysis. Intracellular
calcium measured with fura-2 in single cells covers a wide range (from less
than 2 to 100 nM with a median of 17.6 nM, n = 140 cells). Twenty-one
percent of the cells respond to potassium-induced depolarization with an
increase in intracellular calcium mediated by influx of extracellular
calcium. The L-type calcium channel antagonist nimodipine inhibits the
increase in intracellular calcium triggered by membrane depolarization and
blocks small unitary barium currents displaying the characteristics of
L-type calcium currents (unitary conductance of 29 +/- 5 pS in 55 mM BaCl2
and high selectivity for Ba2+ over Na+ and K+) recorded from azolectin
bilayers at the tip of patch pipettes into which isolated olfactory cilia
membrane vesicles had been incorporated. Olfactory neurons are found to be
functionally heterogeneous in their response to membrane depolarization and
can be separated into three groups: one in which the increase in
intracellular calcium is rapid and transient, another in which calcium
increases slowly, and a third group of cells in which depolarization causes
no change in intracellular calcium.
