PROTEIN PHOSPHATASE-1 AND PHOSPHATASE-2A IN TICK SALIVARY-GLANDS AS ASSESSED BY RESPONSES TO OKADAIC ACID

Crude protein phosphatase activity was inhibited 80% by nanomolar okad aic acid (OA) in salivary glands of unfed ticks but only 40% in saliva ry glands of feeding ticks. An additional 40% of protein phosphatase w as inhibited by micromolar OA in the salivary glands of feeding ticks but only 10% in salivary glands of unfed ticks. Cyclic AMP and OA alon e or together increased the phosphorylation of multiple proteins in a plasma membrane-enriched 900 g supernatant fraction of tick salivary g lands. Exogenous cyclic AMP stimulated increased incorporation of phos phate into proteins with approximate molecular weights of 109, 70, 64, 51, 48, 42 and 18.5 kDa. Micromolar OA in the absence of exogenous cy clic AMP stimulated increased incorporation of phosphate into proteins with apparent molecular weights of 109, 93, 74.5, 70, 51, 48, 42 and 18.5 kDa. Cyclic AMP and OA (10(-6) and 10(-9) M) stimulated significa ntly greater phosphorylation of an 18.5 kDa mol. wt protein above that observed in response to stimulation by OA (10(-6) and 10(-9) M) or ex ogenous cyclic AMP alone. Micromolar okadaic acid inhibited the amount and number of proteins but not volume of saliva secreted by whole tic ks in response to stimulation by DA and theophylline. However, micromo lar and nanomolar okadaic acid inhibited the ability of dopamine to st imulate fluid secretion by isolated salivary glands. Overall, the data support the existence of type 1 and 2A protein phosphatases in tick s alivary glands and a role for protein phosphatases in modulating tick salivary secretion.