okadaic-acid and 2-aminoethoxydiphenyl-borate

Using a combination of fluorescence measurements of intracellular Ca(2+) ion concentration ([Ca(2+)](i)) and membrane potential we have investigated the sensitivity to serine/threonine phosphatase inhibition of Ca(2+) entry stimulated by activation of the Ca(2+) release-activated Ca(2+) (CRAC) entry pathway in rat basophilic leukemia cells. In both suspension and adherent cells, addition of the type 1/2A phosphatase inhibitor calyculin A, during activation of CRAC uptake, resulted in a fall in [Ca(2+)](i) to near preactivation levels. Pre-treatment with calyculin A abolished the component of the Ca(2+) rise associated with activation of CRAC uptake and inhibited Mn(2+) entry, consistent with a requirement of phosphatase activity for activation of the pathway. Depletion of intracellular Ca(2+) stores is accompanied by a large depolarisation which is absolutely dependent upon Ca(2+) entry via the CRAC uptake pathway. Application of calyculin A or okadaic acid, a structurally unrelated phosphatase antagonist inhibits this depolarisation. Taken in concert, these data demonstrate a marked sensitivity of the CRAC entry pathway to inhibition by calyculin A and okadaic acid.

Topics: Animals; Boron Compounds; Calcium; Calcium Signaling; Cations, Divalent; Cells, Cultured; Enzyme Inhibitors; Ion Transport; Leukemia, Basophilic, Acute; Manganese; Marine Toxins; Membrane Potentials; Okadaic Acid; Oxazoles; Phosphoprotein Phosphatases; Protein Phosphatase 1; Rats; Thapsigargin