The long-term goal of this work is to understand how vestibular organs, which transduce head position and movement, function and develop. Good health depends on the normal function of these organs. Damage can lead to debilitating vertigo, dizziness and an inability to maintain steady gaze. The primary afferent neurons to vestibular organs vary in the sensitivity and time course of their responses to head movement stimuli. Some of the variation correlates with region within the sensory organ. In amniotes, a further source of variation is likely to be differences between two classes of sensory hair cell, type I and II. This application proposes to take three approaches to stimulus processing by mammalian vestibular organs, using the rodent utricle as a model. The first aim is to test whether there are regional and cell-type-specific differences in the properties of the hair cell's mechanosensitive transducer conductance, which converts head movement stimuli into the receptor potential. Second, the hair cells' voltage-gated potassium conductances, which shape the receptor potential, will be characterized at the molecular level by applying probes directed at candidate proteins and messenger RNA. These conductances differ substantially between type I and II hair cells. The third aim is to characterize the normal development of hair cells from the period of peak terminal mitoses (prenatal) to birth of the animal. At birth, mouse utricular hair cells express some voltage-gated conductances and ultrastructural analysis shows that although the utricle is immature in many ways, some cells can be recognized as type I or II. The prenatal time course of acquisition of voltage-gated conductances will be determined with whole-cell recording. The expression of voltage-gated potassium channel proteins will be followed in time with molecular probes. Prenatal morphological differentiation of the utricle will be characterized. These experiments should provide insight into early differentiation of hair cells and supporting cells, as well as determine the utility of potassium channel proteins as markers of hair cell differentiation.