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Adrenoceptor‐mediated changes of excitation and contraction in ventricular heart muscle from guinea‐pigs and rabbits.
Author(s) -
Hescheler J,
Nawrath H,
Tang M,
Trautwein W
Publication year - 1988
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1988.sp017024
Subject(s) - stimulation , medicine , contraction (grammar) , endocrinology , calcium , phentolamine , ventricle , muscle contraction , chemistry , guinea pig , biology
1. The influence of alpha‐adrenoceptor stimulation on mechanical and electrophysiological parameters was investigated in ventricular preparations from guinea‐pigs and rabbits. Action potential and force of contraction were measured in papillary muscles and ionic currents were measured in isolated myocytes. 2. The effects of alpha‐adrenoceptor stimulation were compared with those of beta‐adrenoceptor stimulation. 3. In the guinea‐pig the stimulation of alpha‐adrenoceptors caused a small increase in the force of contraction (less than 10% of the response to beta‐adrenoceptor stimulation) which was not accompanied by any increase of the slow calcium inward current. beta‐Adrenoceptor stimulation produced large increases in both force of contraction and slow inward calcium current. The noradrenaline‐induced increase in the slow inward calcium current was not affected by phentolamine. 4. In the rabbit, alpha‐adrenoceptor stimulation produced large increases in the force of contraction (about two thirds of those seen in response to beta‐adrenoceptor stimulation). Whereas beta‐adrenoceptor stimulation also produced large increases in both maximal upstroke velocity of slow‐response action potentials and slow inward calcium current, there was almost no change of both parameters in response to alpha‐adrenoceptor stimulation. 5. We conclude that, first, the contribution of alpha‐adrenoceptors to adrenoceptor‐mediated changes of force of contraction is minimal in the guinea‐pig ventricle, and second, the pronounced changes of force of contraction in the rabbit ventricle in response to alpha‐adrenoceptor stimulation are unrelated to changes in the slow inward calcium current.