title: Cardiac ion channel current modulation by the CFTR inhibitor GlyH-101.
abstract: The role in the heart of the cardiac isoform of the cystic fibrosis transmembrane conductance regulator (CFTR), which underlies a protein kinase A-dependent Cl(-) current (I(Cl.PKA)) in cardiomyocytes, remains unclear. The identification of a CFTR-selective inhibitor would provide an important tool for the investigation of the contribution of CFTR to cardiac electrophysiology. GlyH-101 is a glycine hydrazide that has recently been shown to block CFTR channels but its effects on cardiomyocytes are unknown. Here the action of GlyH-101 on cardiac I(Cl.PKA) and on other ion currents has been established. Whole-cell patch-clamp recordings were made from rabbit isolated ventricular myocytes. GlyH-101 blocked I(Cl.PKA) in a concentration- and voltage-dependent fashion (IC(50) at +100 mV=0.3 ± 1.5 μM and at -100 mV=5.1 ± 1.3 μM). Woodhull analysis suggested that GlyH-101 blocks the open pore of cardiac CFTR channels at an electrical distance of 0.15 ± 0.03 from the external membrane surface. A concentration of GlyH-101 maximally effective against I(Cl.PKA) (30 μM) was tested on other cardiac ion currents. Inward current at -120 mV, comprised predominantly of the inward-rectifier background K(+) current, I(K1), was reduced by ∼43% (n=5). Under selective recording conditions, the Na(+) current (I(Na)) was markedly inhibited by GlyH-101 over the entire voltage range (with a fractional block at -40 mV of ∼82%; n=8). GlyH-101 also produced a voltage-dependent inhibition of L-type Ca(2+) channel current (I(Ca,L)); fractional block at +10 mV of ∼49% and of ∼28% at -10 mV; n=11, with a ∼-3 mV shift in the voltage-dependence of I(Ca,L) activation. Thus, this study demonstrates for the first time that GlyH-101 blocks cardiac I(Cl.PKA) channels in a similar fashion to that reported for recombinant CFTR. However, inhibition of other cardiac conductances may limit its use as a CFTR-selective blocker in the heart.
authors: Cardiovascular Research Laboratories, School of Physiology and Pharmacology and Bristol Heart Institute, University of Bristol, Bristol BS8 1TD, UK.
authors: Palash P
authors: PP
authors: Barman
authors: Stéphanie C M
authors: SC
authors: Choisy
authors: Hanne C
authors: HC
authors: Gadeberg
authors: Jules C
authors: JC
authors: Hancox
authors: Andrew F
authors: AF
authors: James
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology; D002478:Cells, Cultured; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors*; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006834:Hydrazines / Q000494:pharmacology*; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors / Q000502:physiology; D011817:Rabbits; D015222:Sodium Channels / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; D006834:Hydrazines; C548779:N-(2-naphthalenyl)-((3,5-dibromo-2,4-dihydroxyphenyl)methylene)glycine hydrazide; D024661:Potassium Channels, Inwardly Rectifying; D015222:Sodium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005998:Glycine