Acute Changes in Gill Na⁺‐K⁺‐ATPase and Creatine Kinase in Response to Salinity Changes in the Euryhaline Teleost, Tilapia (Oreochromis mossambicus)

Abstract

Some freshwater (FW) teleosts are capable of acclimating to seawater (SW) when challenged; however, the related energetic and physiological consequences are still unclear. This study was conducted to examine the changes in expression of gill Na(+)-K(+)-ATPase and creatine kinase (CK) in tilapia (Oreochromis mossambicus) as the acute responses to transfer from FW to SW. After 24 h in 25 ppt SW, gill Na(+)-K(+)-ATPase activities were higher than those of fish in FW. Fish in 35 ppt SW did not increase gill Na(+)-K(+)-ATPase activities until 1.5 h after transfer, and then the activities were not significantly different from those of fish in 25 ppt SW. Compared to FW, the gill CK activities in 35 ppt SW declined within 1.5 h and afterward dramatically elevated at 2 h, as in 25 ppt SW, but the levels in 35 ppt SW were lower than those in 25 ppt SW. The Western blot of muscle-type CK (MM form) was in high association with the salinity change, showing a pattern of changes similar to that in CK activity; however, levels in 35 ppt SW were higher than those in 25 ppt SW. The activity of Na(+)-K(+)-ATPase highly correlated with that of CK in fish gill after transfer from FW to SW, suggesting that phosphocreatine acts as an energy source to meet the osmoregulatory demand during acute transfer.

Cellular distributions of creatine kinase in branchia of euryhaline tilapia (Oreochromis mossambicus)

“…The CK system (likely MM-CK) is directly functionally coupled with Na ϩ -K ϩ -ATPase, which allows ATP generated by membrane-bound CK to be directly channeled to the ATPase without equilibration with the cytosolic bulk phase in G. mirabilis gills. CK activity is ϳ80 times higher than that of Na ϩ -K ϩ -ATPase in tilapia gills (37). The results obtained elsewhere (37) and in the present study appear to support the hypothesis that a coordinated upregulation of Na ϩ -K ϩ -ATPase and MM-CK occurs in tilapia MR cells.…”

“…CK activity is ϳ80 times higher than that of Na ϩ -K ϩ -ATPase in tilapia gills (37). The results obtained elsewhere (37) and in the present study appear to support the hypothesis that a coordinated upregulation of Na ϩ -K ϩ -ATPase and MM-CK occurs in tilapia MR cells. Furthermore, Kultz and Somero (15) also demonstrated the existence of all the other CK isoforms, including mitochondria CK, in G. mirabilis gills, suggesting the existence of a complete phosphocreatine shuttle.…”

“…The first is a crisis phase, in which fish critically respond to the removal of water from the gill and the gut epithelia (dehydration), and the second phase is stabilization, during which the fish remains alive or dies, according to the extent of dehydration (1,12,14). Tilapia died within 4 h after being directly transferred to SW (35 ppt); however, they survived after transfer from FW to 25-ppt SW (14,37). Fish must expend much energy to react to and compensate for a salinity challenge, particularly in the gill, intestine, kidney, and brain.…”

“…Various CK isoforms retain a phosphocreatine energy shuttle by which ATP generated by oxidative phosphorylation in mitochondria CK produces creatine phosphate, which is then transported to the cytosol and used by the cytosolic CK (MM, MB, or BB) to regenerate ATP at sites of high energy consumption. After the fish is transferred from a hypotonic (freshwater) to a hypertonic (seawater) medium, CK, especially the muscle-form of CK in the tilapia gill, can be affected by salinity, directly or indirectly (37). Interestingly, the altered MM-type CK after seawater transfer seems to be a newly synthesized protein that is involved in osmoregulation.…”

Supplementation of enzyme-treated soy protein saves dietary protein and promotes digestive and absorptive ability referring to TOR signaling in juvenile fish

“…Hepatopancreas and intestine protein concentration were determined by the method of Bradford (1976). Trypsin and chymotrypsin activities were assayed according to Hummel (1959); lipase and amylase activities were determined as described by Furne et al (2005), and the activities of Na + /K + -ATPase, γ-GT, and AKP were determined according to the procedure described by Weng et al (2002), Bauermeister et al (1983), and Hu et al (2014), respectively.…”