Abstract
In previous publications it was reported that barium in concentrations from 0.5 to 20 mM induced tension development in isolated guinea pig taenia coli, which response was dependent on the presence of external calcium (1), and that total Ca content did not change but 45Ca uptake of the cellular fraction which did not exchange within 4 minutes increased above control level during Ba-induced tension development (2). It was also mentioned that Ba increased Ca entry in taenia coli and that this Ca probably plays an essential role during tension development (2).
On the other hand, hypertonically added 40 mM K-induced tonic tension development in taenia coli was noted to be composed of phasic and tonic phases and it was proposed that in the phasic contraction, sufficient Ca is released from a cellular site to initiate contraction, whereas in the tonic contraction enough Ca crosses the membrane to initiate and also to maintain contraction(3). However, the movement of Ca in the above processes has not been studied systematically. This work was undertaken to study the movement of Ca in taenia coli during Ba- and high-K-induced tension developments by investigating the total Ca, 45Ca uptake and efflux and 45Ca uptake of the cellular fraction which did not exchange within 4 minutes.
A part of this work has already been reported (2, 4).
