Mg2+-dependent phosphatase as an inhibitory mediator of the nonselective cation current induced by aluminum fluoride in guinea-pig chromaffin cells.
Internal administration of the G protein activator, guanosine-5'-o-(3-thiotriphosphate) (GTP gamma S) or aluminum fluoride (AIF) complex, produced an inward nonselective cation current (INS) at -55 mV. This current was rapidly diminished under conditions of high intracellular Mg2+ ([Mg2+] = 979 microM), the half decay time (T1/2) being 80 to 100 s. As [Mg2+] in AlF solutions decreased from 400 to 12 microM, the maximum amplitude of AlF-induced INS became larger and the current was diminished more slowly. The AlF INS in the presence of 12 microM Mg2+ reversed polarity at about +9 mV, irrespective of the extent of decline. Bath application of muscarine produced a sustained INS in the absence of AlF complex, but in its presence, the overall current comprising a spontaneously developed INS and muscarine-induced INS was rapidly diminished. Addition of vanadate (0.5 mM) to 979 microM Mg2+ -containing AlF solution mimicked the effects of low Mg2+ solution. Inversely, addition of alkaline phosphatase (40 units/ml) to 12 microM Mg2+ AlF solution reproduced the effects of high Mg2+ solution. It is suggested that AlF complex deactivates INS through facilitating an apparent activity of Mg2+ -dependent phosphatase.
Inoue
M
M
Department of Physiology, School of Medicine, Fukuoka University, Japan.
Fujishiro
N
N
Imanaga
I
I
D017607:Aluminum Compounds / Q000494:pharmacology*; D000818:Animals; D002412:Cations / Q000378:metabolism; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005459:Fluorides / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D009116:Muscarine / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D000071636:Protein Phosphatase 2C
D017607:Aluminum Compounds; D002412:Cations; D007473:Ion Channels; D018721:Muscarinic Agonists; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009116:Muscarine; D006160:Guanosine Triphosphate; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C; D008274:Magnesium; D005459:Fluorides; C032311:aluminum fluoride