- Email: [email protected]
Adenylate cyclase-coupled adenosine receptors in the heart: A reevaluation
J Mol Cell Cardiol 17 (Supplement 3) (1985) 1 7 2 ON FELODIPINE AND ITS INTERACTIONS WITH TWO Ca-AGONISTS, H 160/51 AND BAY K 8644. P. Gj~rstrup and H. H~rding, Department of Pharmacology and Biochemistry, H~ssle Cardiovascular Research Laboratories, S-431 83 MDlndal, Sweden. Felodipine is a Ca-antagonistic dihydropyridine, which in its inhibitory action displays a 100-fold selectivity for vascular over cardiac muscle. The aspect of its selectivity has now been further studied on electrically driven papillary muscles from cat and spontaneously active rat portal veins in vitro. In papillary muscles H 160/51 and Bay K 8644 had the same high efficacy as isoprenaline with EC50:s of 1.5"10 -6 and 8"10 -8 M, respectively. In portal veins approximately the same EC50:s were obtained, but the maximal responses were only around 20% of the maximum obtained with noradrenaline. Experiments were then repeated in the presence of felodipine; concentrations were chosen to obtain a decrease in activity by 25-75% in each tissue (I0-7~i0 -6 M for papillary muscles and 10-9-10 -8 M for portal veins). In papillary muscles felodipine caused a rightward shift in dose response curves for both agonists, while in the portal vein felodipine did not affect the responses to either agonist. The results may suggest separable sites of actions for dihydropyridines in vessels, but not in cardiac tissue.
173PHYSICAL E X E R C I S E IN PREVE~T'rYN$ ~(USCLES A N D ~VOCAI~DIU~[ C H A F q E S l~! T~ATS U N D E ~ H Y P O K I N E S I A . Y. G. Z o r b a s , G. L. N i z a m o v . ! ~ n i e l o p o l u I n s t i t u t e of Physiology, Bucharest, Rumania. It has b e e n d e m o n s t r a t e d that h y p o k i n e s i a ( d i m i n i s h e d m u s c u l a r a c t i vity) i n d u c e s n u m e r o u s c h a n g e s in d i f f e r e n t o r g a n s and s y s t e m s , i n c l u d i n g that of ca~'diovascular s y s t e m . & g a i n s t this b a c k g r o u n d the o b j e c t i v e of this i n v e s t i g a t i o n was to e v a l u a t e the e f f i c a c y of p h y s i c a l e x e r c i s e (PE) for p r e v e n t i n g the d e v e l o p m e n t of a l t e r a t i o n s in the s k e l e t a l m u s c l e s and m y o a c d i u m om 159 a l b i n o r a t s under d i f f e r e n t p e r i o d s of h y p o k i n e s i a (HK). For the s i m u l a t i o n of ~TK the e x p e r i m e n t a l g r o u p of r a t s were k e p t in s m a l l i n d i v i d u a l cages made of p l e x i g l a s , and the c o n t r o l r a t s were p l a c e d u n d e r o r d i n a r y v i v a r i u m c o n d i t i o n s . S w i m m i n g in w a t e r w i t h a t e m p e r a t u r e of 3 1 - 3 2 ~ was u s e d as a m e a n of PE. All rats were feed a complete diet w i t h w a t e r ad lib. T h e y were d e c a p a c i t a t e d on the 15th, 30th, 6 0 t h a n d 9 0 t h days of the e x p e r i m e n t a l period. The v e n t r i c u l a r m y o c a r d i u m and t i s s u e of s k e l e t a l m u s c l e s from the p o s t e r i o r g r o u p of f e m o r a l m u s c l e s were e x a m i n e d . I!ydroxyproline, h e x o s a m i n e s and h e x u r o n i c a c i d in h y d r o l y s a t e s of dry t i s s u e a c e t o n e p o w d e r were a s s a y e d . The o b t a i n e d r e s u l t s were p r o c e s s e d s t a t i s t i c a l l y . The p a r a m e t e r s u n d e r s t u d y were e x h i b i t e d s u b s t a n t i a l a l t e r a t i o n s . It was c o n c l u d e d that PE cannot be u s e d to p r e v e n t s c l e r o t i c c h a n g e s in m u s c l e s of rats under h y p o k m n e s i a .
1 7 4 A D E N Y L A T E CYCLASE-COUPLED ADENOSINE RECEPTORS IN THE HEART: A REEVALUATION. W. SchGtz, M. Freissmuth, V. Hausleithner. Institute of Pharmacology, University of Vienna, A-1090 Vienna, Austria. The underlying mechanism for the cardiac depressant action of adenosine (AR) is a great matter of controversy. No definite conclusion can be drawn to date whether myocardial AR receptor binding triggers off adenylate cyclase (AC) inhibition. In the present study the influence of AR on cardiac ventricular AC of guinea pigs was investigated in a more homogeneous sarcolemmal membrane preparation than previously used. Microsomal particles obtained by differential centrifugation were further fractionated on a shallow self-forming gradient of Percoll. Along the gradient identical peaks were identified for specific [3H]ouabain, [125I]cyanopindolol, and [125I] (-)N6hydroxy-phenylisopropyladenosine binding and for AC activity, which occurred at a density of 1.032. However, the peak of 5'-nucleotidase activity was at a slightly higher density (1.035) and closely coincided with the activity peak of angiotensin I converting enzyme, a marker for endothelial plasma membranes. Inhibition of AC by N6-cyclo hexyladenosine, as measured in each fractionation step following homogenization, was only significant at the gradient peak of the enzyme. Analysis of the degree and rank order of potency of AR receptor agonists and antagonists on AC activity in the peak fraction was suggestive for interaction with A1-AR receptors. Hence, AR-induced AC inhibition in the heart seems only demonstrable if contamination of the sarcolemmal preparation with other cellular membrane components is kept at a minimum.
~v
173PHYSICAL E X E R C I S E IN PREVE~T'rYN$ ~(USCLES A N D ~VOCAI~DIU~[ C H A F q E S l~! T~ATS U N D E ~ H Y P O K I N E S I A . Y. G. Z o r b a s , G. L. N i z a m o v . ! ~ n i e l o p o l u I n s t i t u t e of Physiology, Bucharest, Rumania. It has b e e n d e m o n s t r a t e d that h y p o k i n e s i a ( d i m i n i s h e d m u s c u l a r a c t i vity) i n d u c e s n u m e r o u s c h a n g e s in d i f f e r e n t o r g a n s and s y s t e m s , i n c l u d i n g that of ca~'diovascular s y s t e m . & g a i n s t this b a c k g r o u n d the o b j e c t i v e of this i n v e s t i g a t i o n was to e v a l u a t e the e f f i c a c y of p h y s i c a l e x e r c i s e (PE) for p r e v e n t i n g the d e v e l o p m e n t of a l t e r a t i o n s in the s k e l e t a l m u s c l e s and m y o a c d i u m om 159 a l b i n o r a t s under d i f f e r e n t p e r i o d s of h y p o k i n e s i a (HK). For the s i m u l a t i o n of ~TK the e x p e r i m e n t a l g r o u p of r a t s were k e p t in s m a l l i n d i v i d u a l cages made of p l e x i g l a s , and the c o n t r o l r a t s were p l a c e d u n d e r o r d i n a r y v i v a r i u m c o n d i t i o n s . S w i m m i n g in w a t e r w i t h a t e m p e r a t u r e of 3 1 - 3 2 ~ was u s e d as a m e a n of PE. All rats were feed a complete diet w i t h w a t e r ad lib. T h e y were d e c a p a c i t a t e d on the 15th, 30th, 6 0 t h a n d 9 0 t h days of the e x p e r i m e n t a l period. The v e n t r i c u l a r m y o c a r d i u m and t i s s u e of s k e l e t a l m u s c l e s from the p o s t e r i o r g r o u p of f e m o r a l m u s c l e s were e x a m i n e d . I!ydroxyproline, h e x o s a m i n e s and h e x u r o n i c a c i d in h y d r o l y s a t e s of dry t i s s u e a c e t o n e p o w d e r were a s s a y e d . The o b t a i n e d r e s u l t s were p r o c e s s e d s t a t i s t i c a l l y . The p a r a m e t e r s u n d e r s t u d y were e x h i b i t e d s u b s t a n t i a l a l t e r a t i o n s . It was c o n c l u d e d that PE cannot be u s e d to p r e v e n t s c l e r o t i c c h a n g e s in m u s c l e s of rats under h y p o k m n e s i a .
1 7 4 A D E N Y L A T E CYCLASE-COUPLED ADENOSINE RECEPTORS IN THE HEART: A REEVALUATION. W. SchGtz, M. Freissmuth, V. Hausleithner. Institute of Pharmacology, University of Vienna, A-1090 Vienna, Austria. The underlying mechanism for the cardiac depressant action of adenosine (AR) is a great matter of controversy. No definite conclusion can be drawn to date whether myocardial AR receptor binding triggers off adenylate cyclase (AC) inhibition. In the present study the influence of AR on cardiac ventricular AC of guinea pigs was investigated in a more homogeneous sarcolemmal membrane preparation than previously used. Microsomal particles obtained by differential centrifugation were further fractionated on a shallow self-forming gradient of Percoll. Along the gradient identical peaks were identified for specific [3H]ouabain, [125I]cyanopindolol, and [125I] (-)N6hydroxy-phenylisopropyladenosine binding and for AC activity, which occurred at a density of 1.032. However, the peak of 5'-nucleotidase activity was at a slightly higher density (1.035) and closely coincided with the activity peak of angiotensin I converting enzyme, a marker for endothelial plasma membranes. Inhibition of AC by N6-cyclo hexyladenosine, as measured in each fractionation step following homogenization, was only significant at the gradient peak of the enzyme. Analysis of the degree and rank order of potency of AR receptor agonists and antagonists on AC activity in the peak fraction was suggestive for interaction with A1-AR receptors. Hence, AR-induced AC inhibition in the heart seems only demonstrable if contamination of the sarcolemmal preparation with other cellular membrane components is kept at a minimum.
~v