Poster abstracts

Poster number 66 submitted by Haiyan Liu

ACTH and cAMP Inhibit bTREK-1 K+ Channels Through A PKA Independent Mechanism

Haiyan Liu (department of neuroscicence), Judith A. Enyeart (department of neuroscicence), John J. Enyeart (department of neuroscicence)

Abstract:
Bovine adrenal zona fasciculate (AZF) cells express the two-pore/four transmembrane segment (2P/4TMS) bTREK-1 K+ channels. These channels set the resting membrane potential and link adrenocorticotropic hormone (ACTH) receptor activation to membrane depolarization and cortisol secretion. Whole cell patch clamp recording showed that protein kinase A (PKA) inhibitors, PKI (6-22) amide and H-89 failed to reduce the inhibition of bTREK-1 by both ACTH and forskolin. An ACTH derivative, O-nitrophenyl sulfenyl-ACTH inhibited bTREK-1 at concentrations which produced little or no activation of PKA. EPAC2 (a guanine nucleotide exchange factor activated by cAMP) is highly expressed in AZF cells and can be selectively activated by 8-CPT-2'-O-Me-cAMP. When patch clamp recordings were made with pipette solutions that contained 8-CPT-2'-O-Me-cAMP, bTREK-1 was inhibited with an IC50 of 0.63 micromolar, a concentration which produced no activation of PKA in these cells. The inhibition of bTREK-1 by 8-CPT-2'-O-Me-cAMP required ATP hydrolysis and was unaffected by PKA inhibitors at concentrations that completely blocked PKA activation. 8-CPT-2'-O-Me-cAMP failed to inhibit bTREK-1 channels expressed in HEK 293 cells which do not express EPAC2. These results indicate that ACTH inhibits bTREK-1 K+ channels through cAMP by a PKA independent pathway which may involve activation of EPAC2.

Keywords: bTREK-1, ACTH, Epac