Effects of amiloride in guinea‐pig and rat left atrial contraction as affected by frequency of stimulation and [Ca2+]0‐[Na+]0 ratio: role of Na+/Ca2+exchange

• Published in: British journal of pharmacology 1989-06, Vol.97 (2), p.533-541
• Main Authors: Cargnelli, Gabriella, Bova, Sergio, Luciani, Sisto
• Format: Article
• Language: English
• Subjects: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester - pharmacology; Amiloride - pharmacology; Animals; Biological and medical sciences; Calcium - metabolism; Cardiovascular system; Electric Stimulation; Guinea Pigs; Heart - physiology; In Vitro Techniques; Ion Exchange; Medical sciences; Miscellaneous; Myocardial Contraction - drug effects; Pharmacology. Drug treatments; Rats; Sodium - metabolism; Species Specificity
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1989.tb11982.x

1 The effect of amiloride (0.5 mm) on guinea‐pig and rat left atria driven at various rates of stimulation and different [Ca2+]0‐[Na+]0 ratios has been studied. 2 Amiloride elicited a positive inotropic response in guinea‐pig left atria driven at 0.1 Hz, 0.5 Hz and 1 Hz when [Ca2+]0 was 3.6 mm, 1.8 mm and 0.9 mm respectively but not when [Ca2+]0 was 2.7 mm at 0.1 Hz, 0.9 mm at 0.5 Hz and 0.45 mm at 1 Hz. 3 A positive inotropic response was obtained in guinea‐pig left atria driven at 0.1 Hz and 1 Hz when [Ca2+]0‐[Na+]20 was increased respectively from 8 × 10−5 to 16 × 10−5 and from 2 × 10−5 to 8 × 10−5. The positive inotropic effect was evident only when the ratio was increased by increasing [Ca2+]0 and not by decreasing [Na+]0. 4 In the presence of amiloride, the force of contraction of guinea‐pig left atria decreased instead of increasing, when the rate of stimulation was lowered from 1 Hz to 0.01 Hz. Amiloride inhibited the post‐rest potentiation. 5 In rat left atria amiloride was devoid of any effect in all the above‐mentioned experimental conditions. 6 It is suggested that the pattern of cardiac actions of amiloride can be explained by the inhibition of the Na+/Ca2+ exchange system.