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Muscarinic receptor stimulation and cyclic AMP‐dependent effects in guinea‐pig ventricular myocardium
Author(s) -
Schmied Robert,
Korth Michael
Publication year - 1990
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.1476-5381.1990.tb14716.x
Subject(s) - muscarinic acetylcholine receptor , stimulation , guinea pig , medicine , endocrinology , carbachol , chemistry , cardiology , receptor
1 The effect of carbachol on force of contraction, contraction duration, intracellular Na + activity and cyclic AMP content was studied in papillary muscles of the guinea‐pig exposed to isoprenaline or the phosphodiesterase inhibitor 3‐isobutyl, 1‐methyl xanthine (IBMX). The preparations were obtained from reserpine‐pretreated animals and were electrically driven at a frequency of 0.2 Hz. 2 Isoprenaline (10 n m ) and IBMX (100 μ m ) produced comparable positive inotropic effects of 9.8 and 9.7 mN, respectively. Carbachol (3 μ m ) attenuated the inotropic effects by 82% (isoprenaline) and by 79% (IBMX). The shortening of contraction duration which accompanied the positive inotropic effect of isoprenaline (by 14.9%) and of IBMX (by 22.4%) was not significantly affected by 3 μ m carbachol. 3 The positive inotropic effect of 10 n m isoprenaline and of 100 μ m IBMX was accompanied by an increase in cellular cyclic AMP content of 58 and 114%, respectively. Carbachol (3 μ m ) failed to reduce significantly the elevated cyclic AMP content of muscles exposed to either isoprenaline or IBMX. 4 In the quiescent papillary muscle, isoprenaline (10 n m ) and IBMX (100 μ m ) reduced the intracellular Na + activity by 28 and 17%, respectively. This decline was not influenced by the additional application of 3 μ m carbachol. 5 The results demonstrate that muscarinic antagonism in guinea‐pig ventricular myocardium exposed to cyclic AMP‐elevating drugs is restricted to force of contraction. The underlying mechanism does not apparently involve the cytosolic signal molecule cyclic AMP.