218 P
.C. Castilho et al. J. Exp. Mar. Biol. Ecol. 256 2001 215 –227
Hemolymph osmolality and enzyme activity were subjected to two-way ANOVA followed by Newman–Keuls test.
In all statistical analysis, the significance level adopted was 95 a 5 0.05.
3. Results
1 1
The maximum Na ,K -ATPase activity corresponded to 79.9 3.59 mmol P mg
i 21
21 21
21
protein h
and 86.5 4.92 mmol P mg protein h
of the total ATPase activity
i
in anterior and posterior gills, respectively.
1 1
Some kinetic characteristics of the gill Na ,K -ATPase for both anterior and
posterior gills of crabs acclimated to 2‰ salinity are given in Figs. 1–4. Maximum enzyme activity was a linear function of incubation time Fig. 1A, and protein content
in the 10 000 3 g pellets Fig. 1B, for both gill types. The optimal pH range for maximum enzyme activity in both anterior and posterior gills was 7.6 Fig. 2A. In
anterior gills, temperature influence on enzyme activity was similar in the range of 10–308C Q
5 1.53. On the other hand, its effect on enzyme activity in posterior gills
10
was greater between 10 and 208C Q 5 3.46 than between 20 and 308C Q
5 1.18.
10 10
Further, a significant enzyme inhibition was observed at 408C in both gill types Fig. 2B. Half-saturating concentrations K were estimated for anterior and posterior gills
m 1
21 1
21 21
as follows: Na 5 3.39 and 0.47 mmol l ; K 5 1.14 and 0.61 mmol l
; Mg 5 3.74
21 21
and 2.56 mmol l ; ATP 5 0.84 and 0.65 mmol l
, respectively Fig. 3. The K for
i 21
ouabain was estimated as 0.46 and 0.82 mmol l for anterior and posterior gills,
respectively Fig. 4. During the hyposmotic shock, hemolymph osmolality decreased rapidly, reaching a
1 1
new steady state after approximately 7 days. The Na ,K -ATPase activity of anterior and posterior gills showed an abrupt increase after 1 day of transference. Another
increase in activity was registered, but only in posterior gills, after 15 days of transference Fig. 5A. On the other hand, hemolymph osmolality increased during the
first 3 days of the hyperosmotic shock and a new steady state was attained only 15 days after transference. In this case, enzyme adaptation was also relatively slow. Crabs
transferred to high salinity exhibited a gradual decrease in enzyme activity with complete adaptation occurring only 15 days later Fig. 5B.
4. Discussion and conclusions
