Cellular electrophsyiology of vasculatures in the inner ear

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Summary Blood circulation disturbances contribute to the hearing loss in loud-sound induced trauma, aging, M¿ni¿re's disease, ototoxic drugs and some forms of sudden deafness. Knowledge of inner ear vascular physiology is fundamental to understanding and treating these hearing conditions, but the field remains poorly explored. The long-term goal of this lab is to determine the common and unique patho-physiological mechanisms of cochlear vessels, the key neurohumoral messengers, receptors and channels responsible for cochlear blood flow regulation, and to discover drugs for prevention and treatment of these hearing losses. Our previous studies have found that the cochlear spiral modiolar artery (SMA) has unique vascular tone control mechanisms in resting membrane potential (RP) regulation and neuromuscular transmission. Based on these findings, this proposal sets the following aims: 1) to determine the mechanism and significance that underlie the bi-modal RP distribution of the SMA cells and the mechanism by which ischemia/reperfusion causes the change of the RP distribution and vasotone response; 2) to determine the ion channel(s) and receptor type(s) that mediate the actions of the candidate neurotransmitters (e.g., norepinephrine, acetylcholine, CGRP); 3) to identify the role of candidate neurotransmitters in intrinsic neuromuscular transmission in the SMA. These goals will be achieved through experiments using conventional and whole-cell current- and voltage-clamp recording methods on the in vitro vascular smooth muscle cells (VSMC), plus multiple approaches such as computational modeling, vaso-diameter tracking, nitric oxide production- monitoring, immunocytochemistry, RT-PCR and Western blot analyses. With these studies, we expect to find that the Key channel protein, Kir, co-plays with other persistent membrane currents, such as KATP and Na+-K+-pump currents, to generate the bimodal RP and thus to achieve a high autoregulation capacity of cochlear blood flow. We also anticipate that ischemia/reperfusion treatment will cause up-regulation of nitric oxide production, KATP and Kir expression, and thus cause the RP population shift and the vascular responsiveness change. The novel neuromuscular transmission and various drug effects will be characterized. The knowledge obtained will improve our understanding of how cochlear blood flow is regulated and what are the key factors causing cochlear circulation-deficiency, thus contributing to better prevention and treatment of the circulation-implicated hearing loss, and even the heart attack & stroke.