guanosine-triphosphate and rubidium-chloride

Rubidium and cesium chlorides accelerated cAMP synthesis in rat brain cortex membranes, while other alkali metal chlorides had no influence on the rate of this process. The effect was dose-dependent and yielded above 2-fold activation of adenylate cyclase. It has been shown that Rb+ and Cs+ influenced directly the catalytic subunit of the enzyme and did not substitute Mg2+ in formation of the metal-ATP complex in this reaction. The stimulatory effect of Rb+ was additive to the activation of adenylate cyclase by the half-maximal (0.3 microM) as well as by the saturating (10 microM) forskolin concentrations, pointing to the fact that these effectors activate different isoforms of the enzyme in rat brain cortex.

Topics: Animals; Cerebral Cortex; Cesium; Chlorides; Colforsin; Cyclic AMP; Dose-Response Relationship, Drug; Enzyme Activation; Guanosine Triphosphate; In Vitro Techniques; Magnesium Chloride; Rats; Rubidium

We have used the method of electropermeabilization to measure the dependence of PTH secretion on internal calcium concentration in adult bovine parathyroid cells. The dose-response curve is biphasic, with a peak at 10(-7) M calcium. This result differs significantly from the dose-response curves that have been determined by this method for many other secretory systems, where secretion requires much more calcium and the dependence of secretion on calcium is monotonic. Guanine nucleotide analogs did not modify the calcium dose-response curve of PTH secretion in the electropermeabilized parathyroid cells. The unique properties of adult parathyroid cell secretion are analogous to the unique properties of parathyroid calcium-activated potassium channels, which differ from calcium-activated potassium channels of other cells in that they open at unusually low calcium concentrations and have a peak open probability at about 10(-7) M calcium. We suggest that the opening of these channels in secretory vesicles is required for secretion.

Topics: Adenosine Triphosphate; Animals; Calcium; Cattle; Cell Membrane Permeability; Cells, Cultured; Chlorides; Dose-Response Relationship, Drug; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Kinetics; Parathyroid Glands; Parathyroid Hormone; Rubidium; Thionucleotides