AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 2 250-R256, Copyright © 1984 by American Physiological Society
Are membrane properties essential for the circadian rhythm of Gonyaulax?
H. G. Scholubbers, W. Taylor and L. Rensing
Membrane properties of whole cells of Gonyaulax polyedra were measured by
fluorescence polarization. Circadian changes of fluorescence polarization
exist in exponentially growing cultures. They show an amplitude larger than
that of stationary cultures, indicating that a part of the change is due to
or amplified by an ongoing cell cycle. Measurements of parameters of the
circadian glow rhythm were analyzed for possible correlation with the
membrane data. Considerable differences (Q10 = 2.5-3.0) in fluorescence
polarization were found in cultures kept at different temperatures ranging
from 15 to 27.5 degrees C. The free-running period length at different
temperatures, on the other hand, differed only slightly (Q10 = 0.9-1.1).
Stationary cultures showed higher fluorescence polarization compared with
growing cultures, whereas the free-running period lengths did not differ in
cultures of various densities and growth rates. Temperature steps of
different sign changed the fluorescence polarization slightly in different
directions. The phase shift of 4-h pulses (-5, -9, +7 degrees C) resulted
in maximal phase advances of 4, 6, and 2 h, respectively. The phasing of
the phase-response curves was identical in all these experiments, a finding
not to be expected if the pulses act via the measured membrane properties.
Pulses of drugs that change the fluorescence polarization (e.g.,
chlorpromazine and lidocaine) did not or only slightly phase-shift the
circadian rhythm.
