Submitted on June 8, 2007
Accepted on January 25, 2008
Natriuretic peptides stimulate the cardiac sodium pump via NPR-C coupled NOS activation
Maged William1, Elisha J Hamilton2, Alvaro Garcia3, Henning Bundgaard4, Karin KM Chia5, Gemma A Figtree6, and Helge H Rasmussen6*
1 University of Sydney, Sydney, New South Wales, Australia; Cardiology, Gosford Hospital, Gosford, New South Wales, Australia
2 University of Sydney, Sydney, New South Wales, Australia
3 Cardiology, Royal North Shore Hospital, Sydney, New South Wales, Australia
4 Medical Department, The Heart Centre, Rigshospitalet, National University Hospital, University of Copenhagen, Copenhagen, Denmark; Cardiology, Royal North Shore Hospital, Sydney, New South Wales, Australia
5 North Shore Cardiac Research Centre, University of Sydney, Sydney, New South Wales, Australia
6 University of Sydney, Sydney, New South Wales, Australia; Cardiology, Royal North Shore Hospital, Sydney, New South Wales, Australia
* To whom correspondence should be addressed. E-mail: helger{at}med.usyd.edu.au.
Natriuretic peptides (NP) and their receptors (NPR) are expressed in the heart, but their effects on myocyte function are poorly understood. Because NPRs are coupled to synthesis of cGMP, an activator of the sarcolemmal Na+-K+ pump, we examined if atrial natriuretic peptide (ANP) regulates the pump. We voltage clamped rabbit ventricular myocytes and identified electrogenic Na+-K+ pump current (Ip, arising from the 3:2 Na+:K+ exchange and normalized for membrane capacitance) as the shift in membrane current induced by 100 µmol/L ouabain. Ten nmol/L ANP stimulated the Na+-K+ pump when the intracellular compartment was perfused with pipette solutions containing 10 mmol/L Na+, but had no effect when the pump was at near maximal activation with 80 mmol/L Na+ in the pipette solution. Stimulation was abolished by inhibition of cGMP-activated protein kinase with KT-5823, nitric oxide (NO) activated guanylyl cyclase with 1H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one (ODQ) or NO synthase (NOS) with NG-nitro-L-arginine methyl ester (L-NAME). Since synthesis of cGMP by NPR-A and NPR-B is not NO-dependent or ODQ sensitive we exposed myocytes to AP-811, a highly selective ligand for the NPR-C "clearance" receptor. It abolished ANP induced pump stimulation. Conversely, the selective NPR-C agonist ANP(4-23), reproduced stimulation. The stimulation was blocked by L-NAME. To examine NO production in response to ANP(4-23), we loaded myocytes with the NO-sensitive fluorescent dye diacetylated DAF-2 (DAF-2DA) and examined them by confocal microscopy. ANP(4-23) induced a significant increase in fluorescence which was abolished by L-NAME. We conclude that NP stimulates the Na+-K+ pump via an NPR-C and NO-dependent pathway.
