Abstract
40 mM K-induced isometric contracture of guinea pig taenia coli in the presence of 30 μM dantrolene showed a rapidly rising peak followed by a plateau and then a low sustained tonic contraction. The plateau was delayed by low Ca so that two phasic contractions, fast and slow, were separated from each other. In K-contracture after 15 sec contact with normal Ca following low Ca condition, the fast phasic contraction but not the slow one regained its tension depressed by preceding low Ca, while the slow phasic contraction recovered from its delay. In the presence of 0.2 μM verapamil, K-contracture consisted of the fast phasic contraction without plateau and of the low tonic contraction. The results suggest that K-contracture in the normal state consists of three components, the fast and slow phasic contractions and the tonic contraction, and that dantrolene inhibits a tonic contraction, whereas verapamil inhibits the slow phasic and the tonic contraction. Thus, the contraction curve of each component was tentatively expressed by exponential function, and for simulation of the observed curves a computer was utilized to synthesize the curves using the components of varying parameters. The simulation was successful when based on the above suggestion.
