Article date: June 1989
By: Gabriella Cargnelli, Sergio Bova, Sisto Luciani in Volume 97, Issue 2, pages 533-541
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.
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.
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.
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.
In rat left atria amiloride was devoid of any effect in all the above‐mentioned experimental conditions.
It is suggested that the pattern of cardiac actions of amiloride can be explained by the inhibition of the Na+/Ca2+ exchange system.
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.
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.
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.
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.
In rat left atria amiloride was devoid of any effect in all the above‐mentioned experimental conditions.
It is suggested that the pattern of cardiac actions of amiloride can be explained by the inhibition of the Na+/Ca2+ exchange system.
DOI: 10.1111/j.1476-5381.1989.tb11982.x
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