KCNJ15
Potassium inwardly-rectifying channel, subfamily J, member 15, also known as KCNJ15 is a human gene, which encodes the K4.2 protein. Function. Potassium channels are present in most mammalian cells, where they participate in a wide range of physiologic responses. K4.2 is an integral membrane protein and inward-rectifier type potassium channel. K4.2 has a greater tendency to allow potassium to flow into a cell rather than out of a cell. Three transcript variants encoding the same protein have been found for this gene. The existing literature describing KCNJ15 and K4.2 is sparse. In spite of some initial channel  nomenclature confusion, in which the gene was referred to as Kir1.3 the channel was first cloned from human kidney by Shuck and coworkers in 1997. Shortly thereafter it was shown that mutation of an extracellular lysine residue resulted in 6-fold increase in K current. Two years later, in 1999, voltage clamp measurements in xenopus oocytes found that intracellular acidification decreased the potassium current of K4.2. Also activation of protein kinase C decreased the current although in a non-reversible fashion. Furthermore, it was found that coexpression with related potassium channel K5.1, changed these results somewhat, which the authors concluded  was likely to be a result of heterodimerization. Further voltage clamp investigations found the exact pH sensitivity (pK = 7.1), open probability (high) and conductance of ~25 pS. In 2007 the channel was found to interact with the Calcium-sensing receptor in human kidney, using a yeast-two-hybrid system. This co-localization was verified at the protein level using both immunofluorescence techniques and coimmunoprecipitation of K4.2 and the Calcium-sensing receptor. Also a mutational study of K4.2 has demonstrated that removal of a c-terminal tyrosine increased the K current more than 10-fold. Because the channel has a  very high open probability, the authors of this last article conclude that this increase is mediated by increased trafficking of the protein to the membrane and not increased single-channel conductance. This same line of reasoning is applicable to the initial work of Derst and coworkers. Interactions. KCNJ15 has been shown to interact with Interleukin 16.