Evidence for a new mammalian organ. II. Calcium kinetics

The calcium content and calcium kinetics of the fatty tissue complex comprising the renal sinus organ of the rat kidney are reported. A comparison is made to control brown and white fat in the same animal. The calcium content of the renal sinus tissue is significantly greater than controls. Calcium localization in the mitochondria of the sinus tissue complex is demonstrated. Radioactive isotope studies (45Ca, 85Sr and 99mTc) indicate a dynamic exchange of calcium between the systemic pool and the sinus organ. Active accumulation appears to be operative. Supporting evidence for the existence of a portal vascular system joining the renal sinus complex and the renal parenchyma is presented. The significance of a calcium sink in the renal sinus tissue of the rat kidney is discussed.