Cytoskeleton elements mediate the inhibition of the (Na + +K + )atpase activity by PKC in Rhodnius prolixus malpighian tubules during hyperosmotic shock

In a previous paper, we observed that the specific activity of (Na + +K + )ATPase of the isolated Malpighian tubules from Rhodnius prolixus is inhibited by protein kinase C (PKC) during hyperosmotic shock [Arenstein et al., J Membr Biol 146:47–57 [1995]; Caruso‐Neves et al., Z Naturforsch 53c:911–917 [1998]). In the present paper, we study the involvement of the cytoskeleton in this process using isolated Malpighian tubules of Rhodnius prolixus . We observed that pre‐incubation of the Malpighian tubule cells in hyperosmotic media decreases the specific activity of (Na + +K + )ATPase by 90%. This effect was completely reversed when colchicine, which disrupts microtubules, or cytochalasin B, an inhibitor of actin microfilament polymerization, were added to the media in a dose‐dependent manner. The maximal reversion was obtained with colchicine 7.0 μM or cytochalasin B 5.0 μM. The simultaneous addition of sphingosine 50 ng/mL, an inhibitor of PKC, to 10 μM colchicine or 5 μM cytochalasin B, in hyperosmotic media, did not change the stimulatory effect of these drugs on the specific activity of (Na + +K + )ATPase. On the other hand, the co‐incubation of TPA 20 ng/mL, an activator of PKC, to colchicine or cytochalasin B within hyperosmotic media, abolished the stimulatory effect of these drugs on the specific activity of (Na + +K + )ATPase to a similar extent as hyperosmotic shock. These results suggest that inhibition of the (Na + +K + )ATPase of the isolated Malpighian tubules from Rhodnius prolixus by PKC during hyperosmotic shock is mediated by cytoskeletal elements. Arch. Insect Biochem. Physiol. 48:81–88, 2001. © 2001 Wiley‐Liss, Inc.