A rapid facilitation of acid-sensing ion channels current by corticosterone in cultured hippocampal neurons.

Acid-sensing ion channels (ASIC) play an important role in the central neuronal system and excessive activation of ASICs induces neuronal damage. Recent studies show that ASIC1a, a subunit of ASIC, is involved in stress processes but the mechanisms by which ASIC1a is regulated by corticosterone (CORT), a stress-induced hormone, are as yet unelucidated. In the present study, to explore the effects of CORT on ASIC1a in cultured hippocampal neurons, the whole-cell patch clamp technique was used. We present data showing that extracellular application of 1 and 10 μM CORT increase the inward current when solution of pH 6.0 is applied to the exterior of the cell. Moreover, extracellular application of membrane-impermeable CORT-BSA (1 μM) maintains current elevation induced by the action of ASIC1a. However, intracellular application of CORT (1 μM) did not increase ASIC1a current. Subsequent extracellular application of CORT enhanced the amplitude of ASIC1a current. Also, RU38486 (10 μM), an antagonist of nuclear glucocorticoids receptor, did not block an increase of ASIC1a current induced by CORT. In addition, CORT application further resulted in a significant enhancement of ASIC1a current in the presence of phorbol 12-myristate 13-acetate (0.5 μM) or bryostatin1 (1 μM), which are both protein kinase C (PKC) agonists. On the contrary, after pretreatment with GF109203X (3 μM), an antagonist of PKC, CORT did not elevate ASIC1a current. These data indicate that the rapid increase of ASIC1a current induced by CORT may be caused by the activation of corticosteroid receptors found on the cell membranes of hippocampal neurons and it may involve a PKC-dependent mechanism.