It is well known that the kidney plays a critical role in maintaining extracellular fluid composition and volume. This role is essential for human life. The kidney functions by employing three processes: filtration of large quantities of ultra filtrate across the glomerular filtration barrier; reabsorption of most of the solutes and water; and secretion of certain key substances such as K+, H+, and organic solutes. It is abundantly clear that conductive movement of ions across renal cell membranes plays a key role in solute reabsorption and secretion and in volume regulation. They key focus of this budget period is on the biophysics, regulation, and molecular biology of conductive Ca2+, and K+ movement in the kidney. A model CA+2-activated K+ channel regulation has emerged from more previous studies. This work will be extended to determine the role of calmodulin and protein kinase in regulating these channels. In addition, the role of CA2+ channels and intracellular Ca2+ in regulating CA+2-activated K+ channels will be explored. The properties and regulation of CA +2-activated K+ channels and Ca2+ channels will be studies using single channel patch clamping experiments. The molecular biology of + and Ca2+ channels in the kidney will also be studied. The specific approach is: to determine the cDNA sequence of K+ and Ca2+ channels by cloning either by homology to known channel sequences or by oocyte expression; to determine the properties of renal K+ and Ca2+ channels expressed in Xenopus oocytes; to generate polyclonal antibodies against specific sequences in the channel molecule; to determine the tissue localization of the channels and to assess the role of these channels in renal function. This an important approach because it will provide information at several levels: the molecular structure; nephron localization and function of these channels. Information provided these studies on channel function and molecular biology will be instrumental in increasing our knowledge how solute secretion and absorption occurs normally in the kidney and how renal cells control their volume. It may also will help to increase our knowledge of diseases such as hypertension.