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Regeneration processes in skeletal muscles of the rat
Abstracts 17th Meeting Israel Society for Electron Microscopy
possible reutilization after hormonal binding. We used the n i c o t o n i c - a c e t y l c h o l i n e receptor (AChR) in the electric eel of Torpedo as a model system for neurotransmitters. Pituitary receptors to Gonadotropin Releasing Hormone (GnRH) and gonadal receptors to Luteinizing Hormone (LH) in the rat served as a model for peptide hormones. LH receptors were m a p p e d in the preovulatory follicle. The receptors were not h o m o g e n e o u s l y distributed among the different layers of granulosa cells. They were located mainly in the outer layers, while the oocyte was devoid of specific b i n d i n g sites. This suggests that the hormone exerts its stimulatory effect on the oocyte (to resume its meiosis) indirectly, probably via granulosa cells communicating with the oocyte. LH receptors were localized mainly on the microvilli, both in ovarian granulosa cells and in testicular Leydig cells. Since microvilli are rich in microfilaments, an association of receptor molecules with cytoskeletal elements is suggested. In order to localize the GnRH receptor with its hormone, a decapeptide, which is not fixed in situ by aldehyde, we used a novel m e t h o d of localization using GnRH analogue that after p h o t o a c t i v a t i o n is covalently bound to pituitary gonadotropes. It was found that both the receptor to LH in the granulosa cells, and GnRH in gonadotropes are aggregated following hormonal b i n d i n g and internalized w i t h i n target cells. While m o s t of the i n t e r n a l i z e d receptor-bound hormones in granulosa cells were found in lysosomes, a significant portion of the GnRH-receptor complexes were also found in secretory granules in the target cells. This w o u l d suggest that the LH-bound receptors are degraded after internalization, while some of the G n R H - r e c e p t o r complexes can escape from degradation, and the internalized receptor molecule may be reinserted in the cell membrane. Studies on the A C h R were p e r f o r m e d in order to analyze the orientation of the receptor molecules w i t h i n the cell membrane in the n e u r o m u s c u l a r junction. Using a f f i n i t y - p u r i f i e d antibodies to the receptor, it was found that the receptor molecule is a transmembrane protein. This correlates w e l l with its functioning as a sodium and p o t a s s i u m ion channel. Morphological studies on receptors to neurotransmitters and hormones can thus provide a tool for b e t t e r u n d e r s t a n d i n g of the mode of action of hormones and neurotransmitters in target cells.
333
R E G E N E R A T I O N PROCESSES IN SKELETAL MUSCLES OF THE RAT U. Oron D e p a r t m e n t o f z o o l o g y , The G e o r g e W i s e F a c u l t y o f Life S c i e n c e s , Tel A v i v U n i v e r s i t y , Tel A v i v 69978, Israel
The sequential cytological events of the regeneration process after partial excision of the gastrocnemius muscle was followed by light and electron microscopy. A progressive increase in numbers of nuclei in the cut ends of the damaged fibers and sarcoplasmic outgrowth from others is evident in the injured zone. Numerous m o n o n u c l e a t e d cells fuse with the necrotic cut ends of injured fibers. Other m o n o n u c l e a t e d cells in the entire traumatized area fuse together to give rise to newly formed m u l t i n u c l e a t e d myotubes, that further develop into young striated myofibers during the second week after injury. It is concluded that striated muscle regeneration involves several repair processes, the most prominent b e i n g growth of injured fibers by addition of nuclei and new muscular material and formation of new fibers in a process similar to that of embryonic myogenesis.
U L T R A S T R U C T U R A L ASPECTS OF THE REPAIR PROCESS IN THE M Y O C A R D I U M OF THE WHITE RAT F O L L O W I N G COLD INJURY M. M a n d e l b e r g and U. Oron D e p a r t m e n t of Z o o l o g y , The G e o r g e W i s e F a c u l t y o f L i f e S c i e n c e s , Tel A v i v U n i v e r s i t y , Tel A v i v 69978, Israel
The sequential cytological events of the r e p a i r process in the m y o c a r d i u m of the rat after cold injury to the left ventricle were followed by light and electron microscopy. The traumatized area was initially filled with leucocytes and u n d i f f e r e n t i a t e d m o n o n u c l e a t e d cells. A p p r o x i m a t e l y one week after injury the damaged area was filled mainly with fibroblasts s u r r o u n d e d by collagen fibers. Repair was evident in the margins of the necrotic area. The m y o c a r d i a l cells in this area are c h a r a c t e r i z e d by well developed endonlasmic reticulum, Golgi bodies and many free ribosomes. These cells at first were filled with m i t o c h o n d r i a and a few newly formed myofilaments. Approximately two weeks after injury the m i t o c h o n d r i a were organized in rows between the newly formed myofilaments. The
possible reutilization after hormonal binding. We used the n i c o t o n i c - a c e t y l c h o l i n e receptor (AChR) in the electric eel of Torpedo as a model system for neurotransmitters. Pituitary receptors to Gonadotropin Releasing Hormone (GnRH) and gonadal receptors to Luteinizing Hormone (LH) in the rat served as a model for peptide hormones. LH receptors were m a p p e d in the preovulatory follicle. The receptors were not h o m o g e n e o u s l y distributed among the different layers of granulosa cells. They were located mainly in the outer layers, while the oocyte was devoid of specific b i n d i n g sites. This suggests that the hormone exerts its stimulatory effect on the oocyte (to resume its meiosis) indirectly, probably via granulosa cells communicating with the oocyte. LH receptors were localized mainly on the microvilli, both in ovarian granulosa cells and in testicular Leydig cells. Since microvilli are rich in microfilaments, an association of receptor molecules with cytoskeletal elements is suggested. In order to localize the GnRH receptor with its hormone, a decapeptide, which is not fixed in situ by aldehyde, we used a novel m e t h o d of localization using GnRH analogue that after p h o t o a c t i v a t i o n is covalently bound to pituitary gonadotropes. It was found that both the receptor to LH in the granulosa cells, and GnRH in gonadotropes are aggregated following hormonal b i n d i n g and internalized w i t h i n target cells. While m o s t of the i n t e r n a l i z e d receptor-bound hormones in granulosa cells were found in lysosomes, a significant portion of the GnRH-receptor complexes were also found in secretory granules in the target cells. This w o u l d suggest that the LH-bound receptors are degraded after internalization, while some of the G n R H - r e c e p t o r complexes can escape from degradation, and the internalized receptor molecule may be reinserted in the cell membrane. Studies on the A C h R were p e r f o r m e d in order to analyze the orientation of the receptor molecules w i t h i n the cell membrane in the n e u r o m u s c u l a r junction. Using a f f i n i t y - p u r i f i e d antibodies to the receptor, it was found that the receptor molecule is a transmembrane protein. This correlates w e l l with its functioning as a sodium and p o t a s s i u m ion channel. Morphological studies on receptors to neurotransmitters and hormones can thus provide a tool for b e t t e r u n d e r s t a n d i n g of the mode of action of hormones and neurotransmitters in target cells.
333
R E G E N E R A T I O N PROCESSES IN SKELETAL MUSCLES OF THE RAT U. Oron D e p a r t m e n t o f z o o l o g y , The G e o r g e W i s e F a c u l t y o f Life S c i e n c e s , Tel A v i v U n i v e r s i t y , Tel A v i v 69978, Israel
The sequential cytological events of the regeneration process after partial excision of the gastrocnemius muscle was followed by light and electron microscopy. A progressive increase in numbers of nuclei in the cut ends of the damaged fibers and sarcoplasmic outgrowth from others is evident in the injured zone. Numerous m o n o n u c l e a t e d cells fuse with the necrotic cut ends of injured fibers. Other m o n o n u c l e a t e d cells in the entire traumatized area fuse together to give rise to newly formed m u l t i n u c l e a t e d myotubes, that further develop into young striated myofibers during the second week after injury. It is concluded that striated muscle regeneration involves several repair processes, the most prominent b e i n g growth of injured fibers by addition of nuclei and new muscular material and formation of new fibers in a process similar to that of embryonic myogenesis.
U L T R A S T R U C T U R A L ASPECTS OF THE REPAIR PROCESS IN THE M Y O C A R D I U M OF THE WHITE RAT F O L L O W I N G COLD INJURY M. M a n d e l b e r g and U. Oron D e p a r t m e n t of Z o o l o g y , The G e o r g e W i s e F a c u l t y o f L i f e S c i e n c e s , Tel A v i v U n i v e r s i t y , Tel A v i v 69978, Israel
The sequential cytological events of the r e p a i r process in the m y o c a r d i u m of the rat after cold injury to the left ventricle were followed by light and electron microscopy. The traumatized area was initially filled with leucocytes and u n d i f f e r e n t i a t e d m o n o n u c l e a t e d cells. A p p r o x i m a t e l y one week after injury the damaged area was filled mainly with fibroblasts s u r r o u n d e d by collagen fibers. Repair was evident in the margins of the necrotic area. The m y o c a r d i a l cells in this area are c h a r a c t e r i z e d by well developed endonlasmic reticulum, Golgi bodies and many free ribosomes. These cells at first were filled with m i t o c h o n d r i a and a few newly formed myofilaments. Approximately two weeks after injury the m i t o c h o n d r i a were organized in rows between the newly formed myofilaments. The