Effects of trifluoperazine on function and structure of toad urinary bladder. Role of calmodulin vasopressin-stimulation of water permeability.
Calcium ion plays a major regulatory role in many hormone-stimulated systems. To determine the site of calcium's action in the toad urinary bladder, we examined the effect of trifluoperazine, a compound that binds specifically to the calcium binding protein, calmodulin, and thereby prevents activation of enzymes by the calcium- calmodulin complex. 10 microM trifluoperazine inhibited vasopressin stimulation of water flow, but did not alter vasopressin's effects on urea permeability or short-circuit current. Trifluoperazine also blocked stimulation of water flow by cyclic AMP and methylisobutylxanthine, implying a "postcyclic AMP" site of action. Consistent with these results, trifluoperazine did not decrease epithelial cyclic AMP content or the cyclic AMP-dependent protein kinase activity ratio. Assay of bladder epithelial supernate demonstrated calmodulin-like activity of 1.5 U/microgram protein. Morphologic studies of vasopressin-treated bladders revealed that trifluoperazine did not alter the volume density of cytoplasmic microtubules or significantly decrease the number of fusions between cytoplasmic, aggregate-containing, elongated vesicles and the luminal membrane. Nonetheless, the frequency of luminal membrane aggregates, structures that correlate well with luminal membrane water permeability, was decreased by greater than 50%. Thus, trifluoperazine appears to inhibit the movement of intramembranous particle aggregates from the fused intracellular membranes to the luminal membrane, perhaps by blocking an effect of calcium on microfilament function.
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D002025:Bufonidae; D002118:Calcium / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors*; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D002463:Cell Membrane Permeability / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005260:Female; D008565:Membrane Proteins / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D014268:Trifluoperazine / Q000494:pharmacology*; D001743:Urinary Bladder / Q000187:drug effects*; D014667:Vasopressins / Q000494:pharmacology*; D014882:Water-Electrolyte Balance / Q000187:drug effects
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D008565:Membrane Proteins; D014667:Vasopressins; D014268:Trifluoperazine; D000242:Cyclic AMP; D011494:Protein Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D002118:Calcium