Insulin receptor-related protein (INSRR) is homologous to the insulin receptors. However, proinsulin, insulin, IGF-I, and IGF-II do not stimulate tyrosine phosphorylation of the INSRR, and thus INSRR has been viewed as an orphan receptor []. INSRR is expressed preferentially in the kidney []and functions as an alkali sensor that regulates acid-base balance in the kidney [].