Methylphenidate, but not other CNS stimulants, inhibits red blood cell calcium-activated potassium efflux

Effect of dextroamphetamine and methylphenidate on calcium and magnesium concentration in hyperactive boys

Levels of calcium in plasma, red blood cells, and mononuclear blood cells, levels of calcium in plasma, and the plasma calcium-to-magnesium ratio were measured at baseline and after 3 weeks of each drug phase of a double-blind, placebo-controlled study of methylphenidate and dextroamphetamine in hyperactive boys. Levels of magnesium in plasma were significantly higher after 3 weeks of dextroamphetamine treatment, and the calcium-to-magnesium ratio was significantly lower after 3 weeks of either drug compared with the baseline or placebo condition. There was no change in magnesium levels in red blood cells or mononuclear blood cells. These measures were obtained 30 minutes before the morning dose and at 9 a.m., 9:30 a.m., 10:30 a.m., 11:00 a.m., and noon on the last day of each 3-week phase. Analysis of variance revealed a drug effect on plasma magnesium and on the calcium-to-magnesium ratio but no drug x time interaction. Although these changes were not correlated with the time course of acute symptomatic response to stimulant therapy, the decrease in the ratio may be relevant to side effects and treatment resistance associated with stimulant use.

Continuous measurement of net potassium movements in rat brain cortex suspensions. Effects of glutamate, veratridine, creatine and other substances

Net K fluxes in in vitro suspensions of sliced rat brain cortex were studied by means of a K-sensitive electrode. When incubation was in 3 mM K, a net K efflux occurred. It could be resolved into two first-order rate constants: k1 = 0.486 min-1, and k2 = 0.0102 min-1, that originated from compartments that contained 18% and 82% of tissue K, respectively. k1 Was suppressed by tetrodotoxin (TTX), and k2 was increased 38-fold by veratridine. The latter effect was blocked by TTX, methylphenidate (1 mM), creatine (25 mM), apamin (50 nM), quinine (100 microM), verapamil (22 microM) or D-600 (38 microM). Net K loss was greatly increased by 1 mM ouabain, and enhanced by sodium azide plus iodoacetamide, but not by 0.1 M ethanol. Glutamate (5 mM) induced a considerable and rapid net uptake of K, while aspartate or N-methylaspartate increased K efflux.