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Calcium-Dependent 4-aminopyridine stimulation of protein phosphorylation in squid optic lobe synaptosomes |
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| Authors: | Harish C. Pant Paul E. Gallant Rochelle Cohen Joseph T. Neary Harold Gainer |
| Affiliation: | 1. Laboratory of Preclinical Studies, National Institute on Alcohol Abuse and Alcoholism, 20852, Rockville, Maryland, USA 2. Marine Biological Laboratories, 02543, Woods Hole, Massachusetts, USA 3. Department of Anatomy, College of Medicine, University of Illinois at Chicago, 60612, Chicago, Illinois, USA 4. Laboratory of Biophysics, National Institute of Neurological and Communicative Disorders and Stroke, Marine Biological Laboratory, 02543, Woods Hole, Massachusetts, USA 5. Laboratory of Neurochemistry & Neuroimmunology, National Institute of Child Health and Development, 20205, Bethesda, Maryland, USA |
| Abstract: | When intact synaptosomes were incubated with [gamma-32P]ATP, maximal protein phosphorylation was attained 2 min after the start of incubation. Protein phosphorylation under basal conditions was dependent on external Ca2+, and the dominant peak of phosphorylation was a 50-kd protein. Incubation of intact synaptosomes in the presence of 3-6 mM 4-aminopyridine (4-AP) caused a markedly enhanced phosphorylation of high molecular weight proteins of 90, 100, 130, and 180 kd, with no increase in the 50 or 38 kd proteins. This effect of 4-AP was dependent on external calcium ions in the incubation medium. The 4-AP effect on the high molecular weight proteins was also found in synaptosomal plasma membranes isolated from the synaptosomes. Tetraethylammonium (TEA) ions did not produce this enhancement of phosphorylation. |
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