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Myonemal contraction of Spirostomum I. Kinetics of contraction and relaxation
Author(s) -
Hawkes R. B.,
Holberton D. V.
Publication year - 1974
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1040840209
Subject(s) - contraction (grammar) , biophysics , microinjection , calcium , kinetics , chemistry , stimulus (psychology) , biology , endocrinology , physics , psychology , organic chemistry , quantum mechanics , psychotherapist
A microphotometric method is introduced that allows measurement of the contraction‐relaxation kinetics of Spirostomum in response to electrical stimulation. The time course of contraction includes a rapidly contracting phase of some 4–5 mS during which cells shorten at a rate in excess of 100 cell lengths sec −1 . While a stimulus strength‐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 all‐or‐none event. The kinetics of relaxation following high stimulating voltages and repetitive after contractions also induced by high voltages are explained by excitation‐contraction coupling through a stimulus‐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 −5 M Ca 2+ invariably induces contraction.