- Email: [email protected]
Inhibitory actions of quinidine and quinine on depolarization- and agonist-mediated rat aortic contractions
THE ALTERATION IN,MYOFILAMENTS CALCIUM SENSITIVITY AS A POTENT MECHANISM FOR VASCULAR SMOOTH MUSCLE TONE REGULATION AT HYPOXIA AND GENETIC HYPERTENSION : THE ROLE OF ADENYLATE CYCLASE AND CKINASE PATHWAYS AA.Solo_vLe_v Institute of Pharmacology and Toxicology, 14 Eugene Pottier str., Kiev, 252057 Ukraine.
MECHANISMS OF NEUROPEPTIDE Y POTENTIATION OF SYMPATHETIC CONTRACTION IN THEHUMAN SAPHENOUS VEIN: ROLEOF INTRACELLULARCALCIUM T. Stati, F. Fabi and P. del Basso Department of Pharmacology, Istituto Superiore di Sanit6, Viale Regina Elena 299, 00161 Rome, Italy.
Recently it has been recognized that under a variety of conditions the calcium sensitivity of the contractile system of vascular smooth muscle (VSM) may be altered resulting in a change in the relationship between intraceIlular calcium concentration and contractile force of VSM. In experiments on isolated chemically skined muscular strips of rat portal vien was established that hypoxia shifted the "pCa-tension" relation to the right and decreased the maximal force developed by VSM as comPared to basal level of oxygenation. Addition of cyclic AMP (10-5 M) with theophylline (5 mM) to the buffer solution produced a similar shift to hypoxia. The rate and amplitude of hypoxic relaxation in skinned VSM were decreased by tolbutamide (5 mM), which is known to inh~it cyclic AMP-dependent protein kinases. It was also shown that "pCatension" for skinned aorta and portal vien of spontaneously hypertensive rats (SHR) shifted to the left as compared to normotensive Wistar-Kyoto (WKY) rats. Putative C-kinase inhibitor chelerythrine (10-6 M) shifted "pCa-tension" relation to the right more significantly in SHR than in WKY. Chelerythrine sharply reduced the maximal tension developed by VSM in SHR whilst causing a non-significant decrease in tension of VSM from WKY rats. We suggest that the lowering pO2 c,'m alter myofilaments sensitivity to calcium and this effect may be related to cyclic AMP-dependent phosphorylation of myosin light chain kinase and its inactivation. The increase of myofilamcnts calcium sensitivity in SHR may be linked with the increase of C-kinase activity in vascular wall.
The mechanism underlying the potentiating effect of NPY on the contractile responses induced by noradrenaline (NA) and by sympathetic stimulation until now remains uncertain. In order to verify the role of intra- and extra-celMar calcium on NPY potentiation, we examined the effects of the inhibitor of sarcoplasmic reticulum Ca ++ pump Thapsigargin and, respectively, of the calcium channel blocker Verapamil on the contractile responses to NA and to transmural nerve stimulation (TNS) in human saphenous veins, isometric responses of superfused ring segments of the veins were recorded according to t h e previously described method (Br, J. Pharmacot., "110,338-342, 1993). TNS was delivered via platinum wire electrodes placed on both sides of the vessel (1 min, 14 V, 0.3 ms, 1-16 Hz). Infusions of NA (0.1-3 gM for 1 min) were also performed. Contractile-response curves for NA and TNS were obtained. Adding 50 nM NPY to the superfusing medium caused a leftward shift of the frequency- and concentrationresponse curves to TNS and to NA. When Thapsigargin (50 nM) was added to the superfusing medium a potentiating effect on the contractile responses to TNS and to NA was also obtained. In the presence of 10 ~M Verapamil both NPY and Thapsigargin failed to potentiate the contractions induced by NA and TNS. The present data on human saphenous veins suggest that NPY potentiates the vasoconstrictor responses to endogenous and exogenous NA through the mobilization of calcium from sarcoplasmic reticulum~ Calcium entering through verapamilsensitive calcium channels represents a limiting step for this phenomenon.
PHOSPHATIDYLCHOLINE LIPOSOMES THE ABILITY TO SUPPORT VASCULAR MUSKLE CONTRACTILE FORCE UNDER A.V. Stefanov, A.I. Soloviev Institute o f P h a r m a c o l o g y a n d Toxicology, Pottier str., Kiev, 252057 U k r a i n e .
INHIBITORY ACTIONS OF QUINIDINE AND QUININE ON DEPOLARIZATION- AND AGONIST-MEDIATED RAT AORTIC CONTRACTIONS lB. Fernfindez del Pozo, F. P6rez Vizcaino, E. Villamor, 1F. Zaragozfi and J. Tamargo. Dpts. Pharmacology, Sch. Medicine, UCM, 28040 Madrid and 1pharmacognosy, Sch. Pharmacy, UAH.
POSSESS SMOOTH HYPOXIA. 14 E u g e n e
T h e study was u n d e r t a k e n to d e t e r m i n e the effects o f p h o s p h a t i d y l c h o l i n e (PC) liposomes on c o n t r a c t i l i t y o f the isolated segments of the rat p o r t a l v i e n u n d e r hypoxia (pO2 - 3,9 kPa) a n d restored the decreased a m p l i t u d e o f phasic c o n t r a c t i o n s o f V S M b e i n g added to hypoxic solution. T h e y are also redused the degree o f hypoxic relaxation o f V S M preactivated w i t h K + - r i c h solution: a n d p r o m o t e d an increase in the level o f t o n i c t e n s i o n d e v e l o p e d by K + , a c t i v a t e d V S M in h y p a x i c solution. I n c o n c l u s i o n , a n t i h y p o x i c effect o f P C liposomes was suggested to be due to n o t only the m o d i f i c a t i o n of the phospholipid environment of calcium channels and related increase in c a l c i u m p e r m e a b i l i t y o f V S M p l a s m a m e m b r a n e b u t also m a y be d e t e r m i n e d by the d e f e n c e o f calcium channels against lipid p e r o x i d a t i o n p r o d u c t s action. I t is probably t h a t fatty a c i d ti:om liposomes can be used for A T P p r o d u c t i o n in V S M during hypoxia.
The antiarrhythmic drug quinidine has been reported to be a competitive antagonist of c~-adrenoceptors and to inhibit vascular smooth muscle contraction by inhibition of Ca 2+ entry in a voltageand use-dependent manner. The effects of quinidine and its enantiomer, quinine, were compared on isometric contractions in isolated rat aortic rings. Quinidine and quinine relaxed the contractions induced by 80 mM KC1 (pD2s 5.24 ___ 0.05 and 4.21 + 0.09, respectively, P < 0.05), shifted rightwards the concentration-response curves to noradrenaline (pA2 = 6.46 + 0.14 and 5.70 _+ 0.17, respectively, P < 0.05) and at concentrations _ 10-4 M also depressed 'the maximal contractile responses. The contractions induced by oxymetazoline (an alA selective agonist) in rings pretreated with chloroethylclonidine were shifted downwards (with minimal rightward shift) in the presence of quinidine or quinine. These drugs (_> 10-4 M) also shifted the concentrationresponse curves to 5-HT and endothelin-1 downwards and inhibited the contractions induced by 5-HT in Ca2+-free media and those induced by restoring the extracellular Ca 2+ concentration. These results suggested that quinidine and quinine stereoselectively inhibit vascular smooth muscle contractions by Ca 2+ channel blockade, competitive antagonism of al-adrenoceptors (not of the atA- but probably the atD-SUbtype ) and by a non specific effect unrelated to Ca 2+ entry. Supported by a CICYT SAF92-0157 Grant.
-- 252 --
MECHANISMS OF NEUROPEPTIDE Y POTENTIATION OF SYMPATHETIC CONTRACTION IN THEHUMAN SAPHENOUS VEIN: ROLEOF INTRACELLULARCALCIUM T. Stati, F. Fabi and P. del Basso Department of Pharmacology, Istituto Superiore di Sanit6, Viale Regina Elena 299, 00161 Rome, Italy.
Recently it has been recognized that under a variety of conditions the calcium sensitivity of the contractile system of vascular smooth muscle (VSM) may be altered resulting in a change in the relationship between intraceIlular calcium concentration and contractile force of VSM. In experiments on isolated chemically skined muscular strips of rat portal vien was established that hypoxia shifted the "pCa-tension" relation to the right and decreased the maximal force developed by VSM as comPared to basal level of oxygenation. Addition of cyclic AMP (10-5 M) with theophylline (5 mM) to the buffer solution produced a similar shift to hypoxia. The rate and amplitude of hypoxic relaxation in skinned VSM were decreased by tolbutamide (5 mM), which is known to inh~it cyclic AMP-dependent protein kinases. It was also shown that "pCatension" for skinned aorta and portal vien of spontaneously hypertensive rats (SHR) shifted to the left as compared to normotensive Wistar-Kyoto (WKY) rats. Putative C-kinase inhibitor chelerythrine (10-6 M) shifted "pCa-tension" relation to the right more significantly in SHR than in WKY. Chelerythrine sharply reduced the maximal tension developed by VSM in SHR whilst causing a non-significant decrease in tension of VSM from WKY rats. We suggest that the lowering pO2 c,'m alter myofilaments sensitivity to calcium and this effect may be related to cyclic AMP-dependent phosphorylation of myosin light chain kinase and its inactivation. The increase of myofilamcnts calcium sensitivity in SHR may be linked with the increase of C-kinase activity in vascular wall.
The mechanism underlying the potentiating effect of NPY on the contractile responses induced by noradrenaline (NA) and by sympathetic stimulation until now remains uncertain. In order to verify the role of intra- and extra-celMar calcium on NPY potentiation, we examined the effects of the inhibitor of sarcoplasmic reticulum Ca ++ pump Thapsigargin and, respectively, of the calcium channel blocker Verapamil on the contractile responses to NA and to transmural nerve stimulation (TNS) in human saphenous veins, isometric responses of superfused ring segments of the veins were recorded according to t h e previously described method (Br, J. Pharmacot., "110,338-342, 1993). TNS was delivered via platinum wire electrodes placed on both sides of the vessel (1 min, 14 V, 0.3 ms, 1-16 Hz). Infusions of NA (0.1-3 gM for 1 min) were also performed. Contractile-response curves for NA and TNS were obtained. Adding 50 nM NPY to the superfusing medium caused a leftward shift of the frequency- and concentrationresponse curves to TNS and to NA. When Thapsigargin (50 nM) was added to the superfusing medium a potentiating effect on the contractile responses to TNS and to NA was also obtained. In the presence of 10 ~M Verapamil both NPY and Thapsigargin failed to potentiate the contractions induced by NA and TNS. The present data on human saphenous veins suggest that NPY potentiates the vasoconstrictor responses to endogenous and exogenous NA through the mobilization of calcium from sarcoplasmic reticulum~ Calcium entering through verapamilsensitive calcium channels represents a limiting step for this phenomenon.
PHOSPHATIDYLCHOLINE LIPOSOMES THE ABILITY TO SUPPORT VASCULAR MUSKLE CONTRACTILE FORCE UNDER A.V. Stefanov, A.I. Soloviev Institute o f P h a r m a c o l o g y a n d Toxicology, Pottier str., Kiev, 252057 U k r a i n e .
INHIBITORY ACTIONS OF QUINIDINE AND QUININE ON DEPOLARIZATION- AND AGONIST-MEDIATED RAT AORTIC CONTRACTIONS lB. Fernfindez del Pozo, F. P6rez Vizcaino, E. Villamor, 1F. Zaragozfi and J. Tamargo. Dpts. Pharmacology, Sch. Medicine, UCM, 28040 Madrid and 1pharmacognosy, Sch. Pharmacy, UAH.
POSSESS SMOOTH HYPOXIA. 14 E u g e n e
T h e study was u n d e r t a k e n to d e t e r m i n e the effects o f p h o s p h a t i d y l c h o l i n e (PC) liposomes on c o n t r a c t i l i t y o f the isolated segments of the rat p o r t a l v i e n u n d e r hypoxia (pO2 - 3,9 kPa) a n d restored the decreased a m p l i t u d e o f phasic c o n t r a c t i o n s o f V S M b e i n g added to hypoxic solution. T h e y are also redused the degree o f hypoxic relaxation o f V S M preactivated w i t h K + - r i c h solution: a n d p r o m o t e d an increase in the level o f t o n i c t e n s i o n d e v e l o p e d by K + , a c t i v a t e d V S M in h y p a x i c solution. I n c o n c l u s i o n , a n t i h y p o x i c effect o f P C liposomes was suggested to be due to n o t only the m o d i f i c a t i o n of the phospholipid environment of calcium channels and related increase in c a l c i u m p e r m e a b i l i t y o f V S M p l a s m a m e m b r a n e b u t also m a y be d e t e r m i n e d by the d e f e n c e o f calcium channels against lipid p e r o x i d a t i o n p r o d u c t s action. I t is probably t h a t fatty a c i d ti:om liposomes can be used for A T P p r o d u c t i o n in V S M during hypoxia.
The antiarrhythmic drug quinidine has been reported to be a competitive antagonist of c~-adrenoceptors and to inhibit vascular smooth muscle contraction by inhibition of Ca 2+ entry in a voltageand use-dependent manner. The effects of quinidine and its enantiomer, quinine, were compared on isometric contractions in isolated rat aortic rings. Quinidine and quinine relaxed the contractions induced by 80 mM KC1 (pD2s 5.24 ___ 0.05 and 4.21 + 0.09, respectively, P < 0.05), shifted rightwards the concentration-response curves to noradrenaline (pA2 = 6.46 + 0.14 and 5.70 _+ 0.17, respectively, P < 0.05) and at concentrations _ 10-4 M also depressed 'the maximal contractile responses. The contractions induced by oxymetazoline (an alA selective agonist) in rings pretreated with chloroethylclonidine were shifted downwards (with minimal rightward shift) in the presence of quinidine or quinine. These drugs (_> 10-4 M) also shifted the concentrationresponse curves to 5-HT and endothelin-1 downwards and inhibited the contractions induced by 5-HT in Ca2+-free media and those induced by restoring the extracellular Ca 2+ concentration. These results suggested that quinidine and quinine stereoselectively inhibit vascular smooth muscle contractions by Ca 2+ channel blockade, competitive antagonism of al-adrenoceptors (not of the atA- but probably the atD-SUbtype ) and by a non specific effect unrelated to Ca 2+ entry. Supported by a CICYT SAF92-0157 Grant.
-- 252 --