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Differential binding of calcium antagonists to fast and slow-twitch muscles of rats
270
Pharmacological Research. Vol. 22. Supplement 2. 1990
DIFFERENTIAL BINDING OF CALCIUM ANTAGONISTS TO FAST AND SLOW-TWITCH MUSCLES OF RATS M.D.Lograno, E.Daniele, A.De Luca, D.Conte, S.Govoni. Pharmacobiology. Dept., Univ. of Bari Italy. Partially purified preparations of skeletal muscle transverse tubular system (T-system) contain a high concentration of binding sites for dihydropyridines which may be associated with charge movement or with the "voltage sensor". In fact dihydropyridines bind to the T-system, block Tsystem calcium channels, reduce calcium release from the sarcoplasmic reticulum and suppress particular components of the charge movement (Lamb and Walsh, J.Physiol. 393, 595-617, 1987). Electrophysiological data indicate that the slow calcium current is lower in slow-twitch muscles (STM) in comparison with fasttwitch muscles (FTM). Moreover the binding of tritiated isradipine to fiber bundles of FTM is higher then in STM. The present study compares the binding of tritiated isradipine to partially purified preparations of T-system obtained from rat soleus (SOL), a STM, and rat extensor digitorum longus (EDL) , a FTM. Male Sprague Dawley rats were used; EDL and SOL were quickly dissected following decapitation, ho~ogenated in ice cold bicarbonate buffer. Homogenates were filtered on cheese cloth, centrifuged at 3,500 g and the supernatant spun down at 45,000 g. The final pellet was used for binding. Binding was performed using various concentations of labelled isradipine (Amersham). Specific binding was defined using 10 micromolar cold nitrendipine. The results show that EDL express a significantly higher concentration of dihydropyridine binding sites (EDL: Bmax: 50 p.moles/mg of protein, SOL: 2.6 p.moles/mg of protein). The data support the hypothesis that the greater slow calcium current in EDL might be due to an higher number of calcium antagonist-sensitive calcium channels.
104>-6618/90/22110270-0 I/ $03.00/ 0
© 1990 The It alian Pharmacological Societ y
Pharmacological Research. Vol. 22. Supplement 2. 1990
DIFFERENTIAL BINDING OF CALCIUM ANTAGONISTS TO FAST AND SLOW-TWITCH MUSCLES OF RATS M.D.Lograno, E.Daniele, A.De Luca, D.Conte, S.Govoni. Pharmacobiology. Dept., Univ. of Bari Italy. Partially purified preparations of skeletal muscle transverse tubular system (T-system) contain a high concentration of binding sites for dihydropyridines which may be associated with charge movement or with the "voltage sensor". In fact dihydropyridines bind to the T-system, block Tsystem calcium channels, reduce calcium release from the sarcoplasmic reticulum and suppress particular components of the charge movement (Lamb and Walsh, J.Physiol. 393, 595-617, 1987). Electrophysiological data indicate that the slow calcium current is lower in slow-twitch muscles (STM) in comparison with fasttwitch muscles (FTM). Moreover the binding of tritiated isradipine to fiber bundles of FTM is higher then in STM. The present study compares the binding of tritiated isradipine to partially purified preparations of T-system obtained from rat soleus (SOL), a STM, and rat extensor digitorum longus (EDL) , a FTM. Male Sprague Dawley rats were used; EDL and SOL were quickly dissected following decapitation, ho~ogenated in ice cold bicarbonate buffer. Homogenates were filtered on cheese cloth, centrifuged at 3,500 g and the supernatant spun down at 45,000 g. The final pellet was used for binding. Binding was performed using various concentations of labelled isradipine (Amersham). Specific binding was defined using 10 micromolar cold nitrendipine. The results show that EDL express a significantly higher concentration of dihydropyridine binding sites (EDL: Bmax: 50 p.moles/mg of protein, SOL: 2.6 p.moles/mg of protein). The data support the hypothesis that the greater slow calcium current in EDL might be due to an higher number of calcium antagonist-sensitive calcium channels.
104>-6618/90/22110270-0 I/ $03.00/ 0
© 1990 The It alian Pharmacological Societ y