Effects of phenylglyoxal (PGO) and cardiac glycosides, isoprenaline and ryanodine on contractile responses in single fibers from frog ventricle

• Published in: Japanese Journal of Pharmacology 1998, Vol.76 (suppl.2), p.285-285
• Main Authors: Fujino, Sumiko, Fujino, Masako, Fujino, Masahiro
• Format: Article
• Language: English
• ISSN: 0021-5198; 1347-3506
• DOI: 10.1016/S0021-5198(19)41250-X

The present study was done to know the mechanism of positive inetropic effect (PIE) of digoxin (50 nM) and its relation to excitationcontraction (E-C) coupling in cardiac muscle. The fibers were prepared from frog ventricle by enzymatic and mechanical disruption. Developed tensions were measured isometrically.When fibers were immersed in Ringer (22℃) containing 5 mM PGO for 5 min and then washed out in normal Ringer for 30 min, both twitch and K-contracture tensions decreased markedly without affecting caffeine-contracture and resting and action potentials, and also rapid cooling contracture (RCC) tested was weakened. 30 min after PGO. removal, the fibers were immersed in digoxin Ringer for 30 min, both twitch and K-contracture tensions were restored to initial revel, and also RCC was considerably accelerated. The acceleration occurred even in Ca. and Na-deprived Ringer ( pCa 7, choline instead of Na for 3 min), when an immersion in digoxin-Ringer for 30 min preceded. From these results, it could be deduced that (1) digoxin recovers E-C coupling from inhibition due to both PGO.treatment and Ca-and Na deprivation. Digoxigenin, digitoxin and digitoxigenin showed almost the same behavior.