Protein phosphatase 1 and 2A in tick salivary glands as assessed by responses to okadaic acid.

Crude protein phosphatase activity was inhibited 80% by nanomolar okadaic acid (OA) in salivary glands of unfed ticks but only 40% in salivary glands of feeding ticks. An additional 40% of protein phosphatase was inhibited by micromolar OA in the salivary glands of feeding ticks but only 10% in salivary glands of unfed ticks. Cyclic AMP and OA alone or together increased the phosphorylation of multiple proteins in a plasma membrane-enriched 900 g supernatant fraction of tick salivary glands. Exogenous cyclic AMP stimulated increased incorporation of phosphate into proteins with approximate molecular weights of 109, 70, 64, 51, 48, 42 and 18.5 kDa. Micromolar OA in the absence of exogenous cyclic 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 significantly 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 exogenous cyclic AMP alone. Micromolar okadaic acid inhibited the amount and number of proteins but not volume of saliva secreted by whole ticks in response to stimulation by DA and theophylline. However, micromolar and nanomolar okadaic acid inhibited the ability of dopamine to stimulate fluid secretion by isolated salivary glands. Overall, the data support the existence of type 1 and 2A protein phosphatases in tick salivary glands and a role for protein phosphatases in modulating tick salivary secretion.