Kinase Regulation of The Epithelial NA+Channel

The Na channel present in certain kidney epithelia (distal portion of the nephron) is critical to Na reabsorption by the kidneys. Regulation of this channel is an important mechanism that not only affects the final urine Na composition but also total body Na homeostasis. Three subunits of this channel were cloned in 1993 and 1994. This lead to the discovery that mutations of this channel can result in certain types of hypertensive diseases. Thus, an understanding of the regulation of this channel is critical in understanding certain types of channel-related hypertensive diseases. This channel is highly regulated by hormonal and humoral factors. These mode of regulation involve second messenger proteins and kinases, such as protein kinase A and C (PKA and PKC). An understanding of kinase regulation of the cloned channel and its relationship to that found in native epithelia is just beginning. Preliminary data indicates differences between the kinase regulation of the cloned and native channels, a finding that may be attributed to the absence of other uncloned subunits of this channel. Moreover, a detailed understanding of the PKC regulation of the native channel is also lacking. PKC has been implicated in a variety of cellular responses, ranging from the regulation of channel activity to programmed cell death (apoptosis). This diversity of actions of PKC are attributed to the existence of multiple PKC isoforms with distinct cellular functions. It is well established that PKC and its various isoforms are central to the regulation of this channel by a variety of cell signaling cascades, initiated by hormones and other second messengers. However, little is known about their function in epithelia, and none is known about their effect on Na+ channels. This project deals with the elucidation of the roles of the different PKC isoforms in regulation of the cloned channels. The Long term objectives of this proposal are to provide a better in-depth understanding of an important area of channel regulation, along with identification of additional molecules that interact with the cloned channel. These results will pave the way for a better understanding of certain types of channel dysfunction that could result in hypertension, a disease that affects nearly 60 million individuals in the US alone.