J Physiol Volume 586, Number 5, 1307-1319, March 1, 2008 DOI: 10.1113/jphysiol.2007.143818
Role of the cAMP sensor Epac as a determinant of KATP channel ATP sensitivity in human pancreatic β-cells and rat INS-1 cells
Guoxin Kang1,
Colin A. Leech1,
Oleg G. Chepurny1,
William A. Coetzee1,2,3 and
George G. Holz1,3
1 Departments of Physiology and Neuroscience
2 Pediatrics
3 Pharmacology, New York University School of Medicine, New York, NY, USA
Protein kinase A (PKA)-independent actions of adenosine 3',5'-cyclic monophosphate (cAMP) are mediated by Epac, a cAMP sensor expressed in pancreatic β-cells. Evidence that Epac might mediate the cAMP-dependent inhibition of β-cell ATP-sensitive K+ channels (KATP) was provided by one prior study of human β-cells and a rat insulin-secreting cell line (INS-1 cells) in which it was demonstrated that an Epac-selective cAMP analogue (ESCA) inhibited a sulphonylurea-sensitive K+ current measured under conditions of whole-cell recording. Using excised patches of plasma membrane derived from human β-cells and rat INS-1 cells, we now report that 2'-O-Me-cAMP, an ESCA that activates Epac but not PKA, sensitizes single KATP channels to the inhibitory effect of ATP, thereby reducing channel activity. In the presence of 2'-O-Me-cAMP (50 µM), the dose–response relationship describing ATP-dependent inhibition of KATP channel activity (NPo) is left-shifted such that the concentration of ATP producing 50% inhibition (IC50) is reduced from 22 µM to 1 µM for human β-cells, and from 14 µM to 4 µM for rat INS-1 cells. Conversely, when patches are exposed to a fixed concentration of ATP (10 µM), the administration of 2'-O-Me-cAMP inhibits channel activity in a dose-dependent and reversible manner (IC50 12 µM for both cell types). A cyclic nucleotide phosphodiesterase-resistant ESCA (Sp-8-pCPT-2'-O-Me-cAMPS) also inhibits KATP channel activity, thereby demonstrating that the inhibitory actions of ESCAs reported here are unlikely to arise as a consequence of their hydrolysis to bioactive derivatives of adenosine. On the basis of such findings it is concluded that there exists in human β-cells and rat INS-1 cells a novel form of ion channel modulation in which the ATP sensitivity of KATP channels is regulated by Epac.
(Received 24 August 2007;
accepted after revision 10 January 2008;
first published online 17 January 2008)
Corresponding author G. G. Holz: Medical Sciences Building Room 442, 550 First Avenue, New York, NY 10016, USA. Email: holzg01{at}popmail.med.nyu.edu
Copyright © 2008 The Physiological Society.
