Modification of cerebral arterial tone and reactivity by external potassium and magnesium ratio in the dog

The interaction of external potassium ([K^＋]_0) and magnesium ([Mg^<2＋>]_0) ions on the vasoconstrictions induced by these cations was investigated in isolated canine middle cerebral and basilar artetial smooth muscle. In addition, the effects of the [K^＋]_0/[Mg^<2＋>]_0 ratio on the reactivity and contractility to serotonin in these cerebral vascular tissues were examined. The results were similar, irrespective of whether helically-cut strips or rings were utilized. [K^＋]_0 was altered over 0-7.1mM/L and [Mg^<2＋>]_0 between 0-4.8mM/L. The results indicate relationship between the concentration of [K^＋]_0 and degree of vasoconstriction produced upon withdrawal of [Mg^<2＋>]_0 was observed over the range of 1-6mM/L [K^＋]_0. As [K^＋]_0 was increased, stepwise, the slow (s-) phase of the contraction became attenuated, while the magnitude of the fast (F-) phase became progressively smaller. Contractions produced by withdrawal of [K^＋]_0 were modified by [Mg^<2＋>]_0 : the higher the [Mg^<2＋>]_0, the less tension upon withdrawal of [K^＋]_0. Contractility to serotonin was depressed when [K^＋]_0 waslowered