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Effects of amiloride in guinea‐pig and rat left atrial contraction as affected by frequency of stimulation and [Ca 2 +] 0 ‐[Na+] 0 ratio: role of Na+/Ca 2 +exchange
Author(s) -
Cargnelli Gabriella,
Bova Sergio,
Luciani Sisto
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb11982.x
Subject(s) - amiloride , contraction (grammar) , stimulation , guinea pig , medicine , inotrope , endocrinology , chemistry , sodium , organic chemistry
1 The effect of amiloride (0.5 m m ) on guinea‐pig and rat left atria driven at various rates of stimulation and different [Ca 2+ ] 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 [Ca 2+ ] 0 was 3.6 m m , 1.8 m m and 0.9 m m respectively but not when [Ca 2+ ] 0 was 2.7 m m at 0.1 Hz, 0.9 m m at 0.5 Hz and 0.45 m m at 1 Hz. 3 A positive inotropic response was obtained in guinea‐pig left atria driven at 0.1 Hz and 1 Hz when [Ca 2+ ] 0 ‐[Na + ] 2 0 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 [Ca 2+ ] 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 + /Ca 2+ exchange system.