ISSN:
1432-1912
Keywords:
Calcium
;
Verapamil
;
Cyclic AMP
;
Isoprenaline
;
Aminophylline
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Both di-Na-EDTA and verapamil depressed the tension (T) and the maximum rate of rise of tension (dT/dt max) of twitch responses of the isolated hemidiaphragm of the rat to direct electrical stimulation. Depression was preceded by a transient facilitation. The blocking action of di-Na-EDTA was promptly reversed by calcium chloride, whereas the same procedure failed to antagonize the blocking action of verapamil. Isoprenaline and db-cAMP were found to antagonize the blocking action of verapamil. In calcium-free medium verapamil quickly produced block of isometric contractions. The depression of contraction produced by verapamil in calcium-free medium was only slightly or not restored by isoprenaline and db-cAMP. This indicates that the membrane calcium is indispensable for the action of isoprenaline and db-cAMP. The effect of aminophylline on T and dT/dt max depends markedly on calcium in the external medium. In a calcium-free solution, as well as in the presence of verapamil, aminophylline failed to produce, any change in the isometric contraction. It is concluded that the actions of isoprenaline, db-cAMP and aminophylline on the isometric contractions of the isolated hemidiaphragm of the rat produced by direct electrical stimulation are possible only in the presence of an optimal concentration of external calcium and of functionally intact calcium channels in the membrane.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00496184
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