The effect of cobalt on renal tubular electrolyte and water handling was studied in the newt using the method of stationary microperfusion of the proximal and early distal tubules. Na, K, Ca, Mg and ...Cl concentrations were measured by electron probe analysis in tubule samples. 3H inulin was used to estimate the net fluid reabsorption. 5 X 10(-4) M CoCl2 was applied luminally. Proximal perfusion of cobalt increased significantly electrolytes (Na, Cl, Ca, Mg) and net fluid reabsorption. After cobalt injection in distal tubule sodium relative reabsorption was raised by 32%, chloride by 20%, fluid reabsorption by 27%. There was a reduction of calcium and magnesium transport by 8 and 31% accordingly. Potassium reabsorption did not change significantly. These data indicate that the luminal cobalt application stimulates proximal reabsorption and inhibits calcium reabsorption and activates sodium transport in distal tubule.
