Length dependence of staircase potentiation: interactions with caffeine and dantrolene sodium

Citation
De. Rassier et Br. Macintosh, Length dependence of staircase potentiation: interactions with caffeine and dantrolene sodium, CAN J PHYSL, 78(4), 2000, pp. 350-357
Citations number
42
Categorie Soggetti
Pharmacology & Toxicology
Journal title
CANADIAN JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY
ISSN journal
00084212 → ACNP
Volume
78
Issue
4
Year of publication
2000
Pages
350 - 357
Database
ISI
SICI code
0008-4212(200004)78:4<350:LDOSPI>2.0.ZU;2-6
Abstract
In skeletal muscle, there is a length dependence of staircase potentiation for which the mechanism is unclear. In this study we tested the hypothesis that abolition of this length dependence by caffeine is effected by a mecha nism independent of enhanced Ca2+ release. To test this hypothesis we have used caffeine, which abolishes length dependence of potentiation, and dantr olene sodium, which inhibits Ca2+ release. In situ isometric twitch contrac tions of rat gastrocnemius muscle before and after 20 s of repetitive stimu lation at 5 Hz were analyzed at optimal length (L-o), L-o - 10%, and L-o 10%. Potentiation was observed to be length dependent, with an increase in developed tension (DT) of 78 +/- 12, 51 +/- 5, and 34 +/- 9% (mean +/- SEM) , at L-o - 10%, L-o, and L-o + 10%, respectively. Caffeine diminished the l ength dependence of activation and suppressed the length dependence of stai rcase potentiation, giving increases in DT of 65 +/- 13, 53 +/- 11, and 45 +/- 12% for L-o - 10%, L-o, and L-o + 10%, respectively. Dantrolene adminis tered after caffeine did not reverse this effect. Dantrolene alone depresse d the potentiation response, but did not affect the length dependence of st aircase potentiation, with increases in DT of 58 +/- 17, 26 +/- 8, and 18 /- 7%, respectively. This study confirms that there is a length dependence of staircase potentiation in mammalian skeletal muscle which is suppressed by caffeine. Since dantrolene did not alter this suppression of the length dependence of potentiation by caffeine, it is apparently not directly modul ated by Ca2+ availability in the myoplasm.