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¹ University of Rajshahi, Department of Biochemistry and Molecular Biology, Rajshahi-6205, Bangladesh DOI : 10.4194/1303-2712-v11_3_01 Viewed : 3909 - Downloaded : 2439 To characterize whether environmental low temperature is involved in metabolic regulation, Channa punctata species of fish were exposed to cold (4~8°C) for 30 min, 1 hr and 2 hrs since they are much energetic and survive in the critical environment. The inorganic phosphate (Pi) in skeletal muscle was significantly increased after 1 hr in cold compared to control fish kept in ambient temperature, however, although lower, stimulatory response to cold for 2 hrs was also observed. In separate examinations, Na⁺-K⁺ ATPase activity in the extract of skeletal muscle was determined and enhanced significantly after 1 hr and 2 hrs. The results appear to indicate that the increased Pi in response to cold might be due to the higher activity of Na⁺-K⁺ ATPase. To clarify the regulatory mechanism of the enzyme, groups of fish were exposed to cold with 100 mM Na2HAsO4 for 1 hr and 2 hrs. The enhanced Na⁺-K⁺ ATPase activity was reduced significantly when treated with Na₂HAsO₄ compared to the control and also to the respective cold exposed fish. The experimental findings indicate that arsenic is involved in the regulation of cold induced Na⁺-K⁺ ATPase activity. The enhanced Na⁺-K⁺ ATPase activity in skeletal muscle of this species in cold and its inhibition by arsenic may play a critical role in environment. Keywords : Skeletal muscle, arsenic, Na⁺-K⁺ ATPase, sympathetic innervations, cold exposure