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High energy phosphate and total calcium concentrations during ouabain induced myocardial contractures
64 T x A and PGE was c o n t i n u o u s l y a s s a y e d b i o l o g i c a l l y . N i c o t i n e (50 ~M) w a s a d m i n i s t e r e d at intervals. H u m a n p l a t e l e t rich p l a s m a (HPRP) was i n c u b a t e d w i t h nicotine, w i t h and w i t h o u t a d d i t i o n of a r a c h i donic acid (AA), the p r e c u r s o r of T x A and PGE, and the T x A f o r m e d was assayed. N i c o t i n e was found to m a r k e d l y i n c r e a s e the e f f l u x of PGE from the heart, but it did not e l i c i t r e l e a s e of TxA. N i c o t i n e in itself d i d not e l i c i t T x A f o r m a t i o n in the HPRP, n e i t h e r did it a f f e c t the H P R P T x A f o r m a t i o n f r o m AA. It is c o n c l u d e d that n i c o t i n e s t i m u l a t e s a m e c h a n i s m in the AA m e t a b o l i s m that is i n v o l v e d in the PGE b u t not T x A formation.
104.
HIGH E N E R G Y P H O S P H A T E A N D T O T A L C A L C I U M CONC E N T R A T I O N S D U R I N G O U A B A I N I N D U C E D MYOC A R D I A L C O N T R A C T U R E S . A. W i l l i a m s , W.G. Nayler, C a r d i o t h o r a c i c Institute, U n i v e r s i t y of London, England. P e r f u s i o n of i s o l a t e d r a b b i t h e a r t s w i t h b u f f e r s o l u t i o n s c o n t a i n i n g 5 x 10 -6 M o u a b a i n leads to a p o s i t i v e i n o t r o p i c r e s p o n s e f o l l o w e d by the c e s s a tion of d e v e l o p e d t e n s i o n and the onset of tonic contracture, reaching a peak after approximately sixty m i n u t e s p e r f u s i o n w i t h the drug. H e a r t s h a v e b e e n freeze c l a m p e d at v a r i o u s stages of the o u a b a i n i n d u c e d c o n t r a c t u r e s and t i s s u e levels of a d e n o s i n e t r i p h o s p h a t e and c r e a t i n e p h o s p h a t e d e t e r m i n e d by m o n i t o r i n g the p r o d u c t i o n of N A D P H via h e x o k i n a s e and c r e a t i n e kinase catalysed reactions. T i s s u e total c a l c i u m levels w e r e d e t e r m i n e d f o l l o w i n g s o l u b i l i z a t i o n in n i t r i c acid using atomic absorption spectrophotometry. P r e l i m i n a r y r e s u l t s i n d i c a t e a p r o g r e s s i v e depletion of t i s s u e ATP and CP d u r i n g the c o n t r a c t u r e w i t h no s i g n i f i c a n t a l t e r a t i o n in total calcium. This w o r k w a s s u p p o r t e d by a g r a n t from the M e d i c a l R e s e a r c h Council.
104.
HIGH E N E R G Y P H O S P H A T E A N D T O T A L C A L C I U M CONC E N T R A T I O N S D U R I N G O U A B A I N I N D U C E D MYOC A R D I A L C O N T R A C T U R E S . A. W i l l i a m s , W.G. Nayler, C a r d i o t h o r a c i c Institute, U n i v e r s i t y of London, England. P e r f u s i o n of i s o l a t e d r a b b i t h e a r t s w i t h b u f f e r s o l u t i o n s c o n t a i n i n g 5 x 10 -6 M o u a b a i n leads to a p o s i t i v e i n o t r o p i c r e s p o n s e f o l l o w e d by the c e s s a tion of d e v e l o p e d t e n s i o n and the onset of tonic contracture, reaching a peak after approximately sixty m i n u t e s p e r f u s i o n w i t h the drug. H e a r t s h a v e b e e n freeze c l a m p e d at v a r i o u s stages of the o u a b a i n i n d u c e d c o n t r a c t u r e s and t i s s u e levels of a d e n o s i n e t r i p h o s p h a t e and c r e a t i n e p h o s p h a t e d e t e r m i n e d by m o n i t o r i n g the p r o d u c t i o n of N A D P H via h e x o k i n a s e and c r e a t i n e kinase catalysed reactions. T i s s u e total c a l c i u m levels w e r e d e t e r m i n e d f o l l o w i n g s o l u b i l i z a t i o n in n i t r i c acid using atomic absorption spectrophotometry. P r e l i m i n a r y r e s u l t s i n d i c a t e a p r o g r e s s i v e depletion of t i s s u e ATP and CP d u r i n g the c o n t r a c t u r e w i t h no s i g n i f i c a n t a l t e r a t i o n in total calcium. This w o r k w a s s u p p o r t e d by a g r a n t from the M e d i c a l R e s e a r c h Council.