Submitted on December 11, 2006
Accepted on March 12, 2007
Basal and angiotensin II-inhibited neuronal delayed rectifier K+ current
are regulated by thioredoxin
Tomokazu Matsuura1, Rachael Anne Harrison1, Andrew D. Westwell2, Hajime Nakamura3, Anatoly Martynyuk4, and Colin Sumners5*
1 Physiology and Functional Genomics, University of Florida, Gainesville, Florida, United States
2 Medicinal Chemistry, Welsh School of Pharmacy, Cardiff University, Cardiff, Wales, United Kingdom
3 Experimental Therapeutics, Kyoto University Hospital, Kyoto, Sakyo, Japan
4 Anesthesiology, University of Florida, Gainesville, Florida, United States
5 Physiology and Functional Genomics, University of Florida, Gainesville, Florida, United States; Physiology, University of Florida, College of Medicine, Gainesville, Florida, United States
* To whom correspondence should be addressed. E-mail: csumners{at}phys.med.ufl.edu.
In previous studies, we determined that macrophage migration inhibitory factor (MIF), acting intracellularly via its intrinsic thiol-protein oxidoreductase (TPOR) activity, stimulates basal neuronal delayed rectifier K+ current (IKv) and inhibits basal and angiotensin II (Ang II)-induced increases in neuronal activity. These findings are the basis for our hypothesis that MIF is a negative regulator of Ang II actions in neurons. MIF has recently been re-categorized as a member of the thioredoxin (Trx) superfamily of small proteins. In the present study we have examined whether Trx influences basal and Ang II-modulated IKv in an effort to determine whether the Trx superfamily can exert a general regulatory influence over neuronal activity and the actions of Ang II. Intracellular application of Trx (0.8 to 80 nM) into rat hypothalamic/brainstem neurons in culture increased neuronal IKv, as measured by voltage-clamp recordings. This effect of Trx was abolished in the presence of the TPOR inhibitor PMX464 (800 nM). Furthermore, the mutant protein rh (recombinant human) C32S/C35S-Trx, which lacks TPOR activity, failed to alter neuronal IKv. Trx applied at a concentration (0.08 nM) which does not alter basal IKv, abolished the inhibition of neuronal IKv produced by Ang II (100 nM). Given our observation that Ang II increases Trx levels in neuronal cultures, it is possible that Trx (like MIF) has a negative regulatory role over basal and Ang II-stimulated neuronal activity via modulation of IKv. Moreover, these data suggest that TPOR may be a general mechanism for negatively regulating neuronal activity.
