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ON THE SITE OF ACTION OF LANTHANUM IN FROG SARTORIUS MUSCLE

1970; American Society for Pharmacology and Experimental Therapeutics; Volume: 174; Issue: 3 Linguagem: Inglês

10.1016/s0022-3565(25)28649-9

1521-0103

George B. Weiss,

Cardiac electrophysiology and arrhythmias

Experiments were performed to elucidate the mechanism by which lanthanum ion (La+++) acts to alter Ca45 movements and tension responses in frog sartorius muscle. La+++ (1.0 mM) decreased Ca45 uptake but did not appreciably change total Ca++, Na+ or K+ contents. The increase in residual Ca45 space (after a 120-minute washout) usually induced by 80 mM K+ was prevented by La+++, but an increase elicited with caffeine (5.0 mM) was not blocked. Similarly, tension responses to K+ were inhibited by La+++ but responses to caffeine were not. The height and duration of the tension response to 80 mM K+ in a nitrate Ringer's solution was altered by La+++ in a manner analogous to that seen when the K+ concentration was lowered to 32 mM. A transient increase in Ca45 efflux was elicited by La+++ only when the washout solution contained no nonradioactive Ca++. These observations indicate that La+++ acts at some superficial sites located in the sartorius muscle surface and transverse tubule membranes to displace Ca++ and to prevent tension responses and ionic movements associated with these membrane sites. Failure of La+++ to inhibit either increases in residual Ca45 space or contractures produced by caffeine indicates that these effects of caffeine are brought about by mechanisms different from those involved in the similar effects of potassium ion.