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Cardiac ion channel current modulation by the CFTR inhibitor GlyH-101

Barman, Palash P., Choisy, Stéphanie C.M., Gadeberg, Hanne C., Hancox, Jules C., James, Andrew F.
Biochemical and biophysical research communications 2011 v.408 no.1 pp. 12-17
calcium channels, cardiomyocytes, chlorides, cystic fibrosis, electrophysiology, heart, inhibitory concentration 50, potassium, protein kinases, rabbits, sodium
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 (ICₗ.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 ICₗ.PKA and on other ion currents has been established. Whole-cell patch-clamp recordings were made from rabbit isolated ventricular myocytes. GlyH-101 blocked ICₗ.PKA in a concentration- and voltage-dependent fashion (IC₅₀ at +100mV=0.3±1.5μM and at −100mV=5.1±1.3μM). 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 ICₗ.PKA (30μM) was tested on other cardiac ion currents. Inward current at −120mV, comprised predominantly of the inward-rectifier background K⁺ current, IK₁, was reduced by ∼43% (n=5). Under selective recording conditions, the Na⁺ current (INₐ) was markedly inhibited by GlyH-101 over the entire voltage range (with a fractional block at −40mV of ∼82%; n=8). GlyH-101 also produced a voltage-dependent inhibition of L-type Ca²⁺ channel current (ICₐ,L); fractional block at +10mV of ∼49% and of ∼28% at −10mV; n=11, with a ∼−3mV shift in the voltage-dependence of ICₐ,L activation. Thus, this study demonstrates for the first time that GlyH-101 blocks cardiac ICₗ.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.