Abstract
Arginine-vasopressin (AVP) neurons are osmosensory neurons in the brain. So far, it is known that AVP neurons detect an increase in plasma osmolarity by an intake of salt and water and then release vasopressin to regulate plasma osmolarity. Although AVP neurons can regulate plasma osmolarity, it is not known whether they can respond to a hypotonic challenge with activation of Cl − channels and thereby regulate their cell volume. In this study, therefore, we examined functional expression of volume-sensitive Cl− channels and its role in AVP neurons isolated from AVP-enhanced GFP transgenic rats. Swelling-induced currents exhibited phenotypical characteristics of volume-sensitive outwardly rectifying (VSOR) Cl− channel, such as outward rectification, inactivation kinetics at large positive potentials, low-field anion selectivity sequence and inhibition by Cl− channel blockers relatively specific to VSOR. Cell cross-sectional area measurements showed that the cells exhibit a regulatory volume decrease (RVD) and the RVD response was inhibited by VSOR Cl− channel blockers. On the other hand, the amount of AVP secreted was found to be increased in response to osmotic swelling and the swelling-induced AVP secretion was enhanced by the presence of VSOR Cl− channel blockers. These results show that VSOR Cl− channel is expressed in rat AVP neurons and is involved in the RVD response and AVP secretion in hypotonic conditions. [J Physiol Sci. 2008;58 Suppl:S81]
