THE EFFECT OF AZIDE, FLUORIDE, ORTHOVANADATE, AND EDTA SODIUM SALTS ON ECTO-ATPASE ACTIVITY OF RED BLOOD CELLS IN A SCORPIONFISH (SCORPAENA PORCUS L.) AND THORNBACK RAY (RAJA CLAVATA L.)

Abstract

The effect of azide, fluoride, orthovanadate and EDTA sodium salts on the ecto-ATPase activity in red blood cells (RBCs) of a scorpionfish (Scorpaena porcus L.) and thornback ray (Raja clavata L.) was studied. It was shown that under the influence of millimolar (mM) concentrations of the selected biochemical agents, significant differences in the hydrolytic activity of RBC plasma membrane ecto-ATPases were revealed in cartilaginous vs. teleost fish. For example, thronback ray RBC ecto-ATPase was practically insensitive to sodium azide. In contrast, scorpionfish RBC ecto-ATPase was sensitive to sodium azide, which blocked the enzyme activity by 65% at a concentration of 20 mM. Thornback ray RBC ecto-ATPase retained a significant activity (37%) at high (60 mM) concentrations of sodium fluoride, while scorpionfish RBC ecto-ATPase was almost completely blocked at this concentration. EDTA acted as a modifier of thornback ray ecto-ATPase activity: at concentrations of up to 6 mM, ATP hydrolysis was actively blocked (by 58%), and at higher concentrations, ecto-ATPase activity was stimulated (up to 20%). An increase in the EDTA concentration (up to 12 mM) in suspensions of scorpionfish RBCs constantly stimulated the inhibitory effect of the chelator (up to 52% vs. control). The activity of ecto-ATPases in RBCs of the studied fish species was weakly blocked by sodium orthovanadate. These differences may reflect a higher tolerance of thornback ray RBC ecto-ATPase to the effect of the above chemical reagents compared to a scorpionfish. The absence of the sodium azide inhibitory effect on thornback ray RBC ecto-ATPase suggests that this ecto-ATPase may be referred to a family of type 2 ecto-NTPDases (ENTPD2), while scorpionfish ecto-ATPase may belong to type 1 ecto-NTPDases (ENTPD1).