ISSN:
0886-1544
Keywords:
Ciliary motility
;
inclination
;
polarity of beating
;
active sliding velocity
;
sliding translocation rate
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Depolarization-induced cycles of a frontal cirrus of Stylonychia were investigated by applying methods of axial-view analysis of the cilia, high-speed microcinématography, and step voltage-clamp. Rising depolarization (from 3 mV to 7ge; 30mV) increased the rate of beating from zero to maximally 58 Hz. During cyclic activity, the axis of the beat cone of a proximal segment of the cirrus was inclined by 60° (0° = perpendicular to cell surface), and was always oriented 90° counterclockwise to the power stroke. With the stimulus amplitude rising, the orientations of the power stroke and inclination were increasingly shifted in more counterclockwise directions by up to 80° After correction for inclination ( = normalization), and following planification of the track of the segment, we determined the following properties of the cycle during depolarization: The course of the cycle tended to be rounded, i.e., the ratio of major over minor amplitudes (= spatial polarity) approximated a value of 1.6 which is only two thirds of maximal spatial polarity observed during hyperpolarization. The angular velocity generally increased with rising steps of depolarization; up to +5 mV (and comparable to hyperpolarization-induced responses), the velocity maximum occurred during the return stroke. With depolarizations ≥7 mV the angular velocity maximum shifted to the power stroke so that the temporal polarity (rates of power stroke over rates of return stroke) increased from 0.4 to 1.6. Calculations of the angular velocity as referred to the proximal ciliary segment level suggest active sliding rates (between 5 and 30 nm/ms) of identified pairs of doublet microtubules. Ciliary frequency is a function of the rate of reorientation of the cyclic track; this parameter, which corresponds to the rate of translocation of active sliding between pairs of doublets, grew with the amplitude of depolarization. Translocation rates were high during transitions between the beat phases (power stroke, return stroke), and were reduced during these phases. Orientational polarograms of the mean rates of both active sliding and sliding translocation show properties of discreteness as well as continuity. The depolarization-induced changes in inclination, and the inferred patterns of sliding rate and sliding translocation rate, are compared with previous results from hyperpolarization-dependent activation of the same motor organelle.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cm.970160405
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