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+)ATPa se of the isolated Malpighian tubules from Rhodnius prolixus is inhibited b y protein kinase C (PKC) during hyperosmotic shock [Arenstein et al., J Mem br Biol 146:47-57 [1995]; Caruso-Neves et al., Z Naturforsch 53c:911-917 [1 998]). In the present paper, we study the involvement of the cytoskeleton i n this process using isolated Malpighian tubules of Rhodnius prolixus. We o bserved 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 c ytochalasin B, an inhibitor of actin microfilament polymerization, were add ed to the media in a dose-dependent manner. The maximal reversion was obtai ned with colchicine 7.0 muM or cytochalasin B 5.0 muM. The simultaneous add ition of sphingosine 50 ng/mL, an inhibitor of PKC, to 10 muM colchicine or 5 muM cytochalasin B, in hyperosmotic media, did not change the stimulator y 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 colc hicine or cytochalasin B within hyperosmotic media, abolished the stimulato ry effect of these drugs on the specific activity of (Na++K+)ATPase to a si milar extent as hyperosmotic shock. These results suggest that inhibition o f the (Na++K+)ATPase of the isolated Malpighian tubules from Rhodnius proli xus by PKC during hyperosmotic shock is mediated by cytoskeletal elements. (C) 2001 Wiley-Liss, Inc.