Factors influencing 45Ca metabolism in brain and other organs in vivo

The distribution of 45Ca among various tissues of the rat was followed for 8 hr after intravenous administration of the isotope. Three major patterns of 45Ca turnover were demonstrable, represented by: (i) brain; (ii) bone; and (iii) certain soft tissues: kidney, adrenal, and muscle. These differences may be explained in terms of different exchange (e.g., for bone) and physiological barriers (e.g., for brain). Studies on the subcellular distribution of 45Ca in brain, performed 2 hr after intravenous administration of 45CaCl2, showed that mitochondria accumulated 25% of the total 45Ca; moreover, the concentration of the 45Ca accumulated by the mitochondria was decreased by prior administration of phenobarbital and of reserpine, but increased by pentylenetetrazol.