Abstract
The effects of lanthanum ion (La+++) on 45Ca movements and tension responses elicited with nicotine, acetylchohine (ACh) on high potassium ion (K+) were examined in frog rectus abdominis muscle. La+++ (1.0 mM) decreased 45Ca uptake and total Ca++ and Na+ contents, but total K+ contents were increased. Tension responses to K+ (80 mM), ACh (61.6 µM) and nicotine (61.6 µM) were only partially inhibited by La+++. Increases in residual 45Ca spaces (after a 120-minute washout) induced by K+ or ACh were inhibited by La+++, but responses obtained in the presence of nicotine were not altered. In the presence of La+++, total 45Ca spaces were not changed after exposure to K+, nicotine or ACh. Either La+++ or added nonradioactive Ca++ produced both transient increas and smaller sustained increases in 45Ca efflux from muscles previously washed out in Ca-free Binger's solution. Thus, La+++ can replace Ca++ at saturable and superficial membrane sites and. in this manner, may specifically inhibit cellular uptake of 45Ca. The Ca++-dependent action affected by La+++ may be important for initial portion of the contractile responses to K+, nicotine or ACh. It would appear that the Ca++ sources utilized by nicotine to elicit contractile responses in frog rectus abdominis muscle differ in part from those used by K+ and ACh.
Footnotes
- Received December 8, 1971.
- Accepted January 29, 1973.
- © 1973 by The Williams & Wilkins Co.
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