Involvement of Calcium in the Regulation of Serotonin N-Acetyltransferase in Retina |
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Authors: | P Michael Iuvone Joseph C Besharse |
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Institution: | Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, U.S.A.;Department of Emory University School of Medicine, Atlanta, Georgia, U.S.A. |
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Abstract: | The possible involvement of calcium in the regulation of retinal serotonin N-acetyltransferase (NAT) activity was investigated using eye cups of Xenopus laevis cultured in defined medium. Omitting CaCl2 from the culture medium completely inhibited the dark-dependent increase of NAT activity at night. Approximately 10(-4)-10(-3) M free Ca2+ was found to be required for the maximal increase of NAT activity in the dark. Other divalent cations--Ba2+, Sr2+, and Mn2+--did not substitute for Ca2+. Antagonists of voltage-sensitive calcium channels, including nifedipine, methoxyverapamil (D600), Co2+, and Mg2+, were found to be effective inhibitors of the dark-dependent increase of retinal NAT activity. Trifluoperazine also decreased retinal NAT activity. These studies indicate that the increase of retinal NAT activity in the dark is mediated by a specific Ca2+-dependent process and that Ca2+ influx through voltage-sensitive calcium channels is involved. |
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Keywords: | Retina Melatonin Calcium Serotonin N-acetyltransferase |
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