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Myonemal contraction of Spirostomum I. Kinetics of contraction and relaxation

โœ Scribed by R. B. Hawkes; D. V. Holberton

Publisher
John Wiley and Sons
Year
1974
Tongue
English
Weight
842 KB
Volume
84
Category
Article
ISSN
0021-9541

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โœฆ Synopsis

Abstract

A microphotometric method is introduced that allows measurement of the contractionโ€relaxation kinetics of Spirostomum in response to electrical stimulation. The time course of contraction includes a rapidly contracting phase of some 4โ€“5 mS during which cells shorten at a rate in excess of 100 cell lengths sec^โˆ’1^. While a stimulus strengthโ€duration curve determines the threshold of the response, the response to above threshold stimuli of different strengths and to trains of stimuli suggest that contraction of Spirostomum may not be an allโ€orโ€none event. The kinetics of relaxation following high stimulating voltages and repetitive after contractions also induced by high voltages are explained by excitationโ€contraction coupling through a stimulusโ€dependent intermediate effector, possibly the release of calcium ions. Changes in resting membrane potential detected by intracellular recording do not influence the initiation of contraction, while microinjection of calcium buffers above 10^โˆ’5^ M Ca^2+^ invariably induces contraction.

๐Ÿ“œ SIMILAR VOLUMES

Myonemal contraction of Spirostomum. III
Myonemal contraction of Spirostomum. III. The thermal dependence of contraction, relaxation and excitation-contraction coupling
โœ R. B. Hawkes; D. V. Holberton ๐Ÿ“‚ Article ๐Ÿ“… 1976 ๐Ÿ› John Wiley and Sons ๐ŸŒ English โš– 678 KB

## Abstract A microphotometric technique that displays rapid length changes of __Spirostomum__ has been used to follow the variation with temperature of three kinetic parameters of myonemal contraction: contraction rate, relaxation rate and stimulus duration at threshold. In each case the exponenti

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## Abstract In several respects, notably the high velocity of shortening, Ca^2+^ dependence, and ATP independence, contraction of __Spirostomum__ resembles the spasmonemal mechanism of the peritrich ciliates. In this report further mechanical properties of the contractile apparatus are described th

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Electrically stimulated contraction of Spirostomum umbiguum was investigated by high speed cinematography (up to 6,000 pps). Contraction is completed in about 4 msec following a latent period of up to 30 msec. Reduction in length during contraction followed a sigmoid curve, and final length was abou

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## Abstract Measurements made on contraction latencies in __Spirostomum__ suggest that mechanical stimulation causes contractions to be initiated by the release of small amounts of calcium from a store tightly coupled to the contractile apparatus. Contraction to electrical stimulation appears to re