Spironolactone and its main metabolite, canrenoic acid, block human ether-a-go-go-related gene channels.
BACKGROUND
It has been demonstrated that spironolactone (SP) decreases the QT dispersion in chronic heart failure. In this study, the effects of SP and its metabolite, canrenoic acid (CA), on human ether-a-go-go-related gene (HERG) currents were analyzed.


RESULTS
HERG currents elicited in stably transfected Chinese hamster ovary cells were measured with the whole-cell patch-clamp technique. SP decreased HERG currents in a concentration-dependent manner (IC50=23.0+/-1.5 micromol/L) and shifted the midpoint of the activation curve to more negative potentials (Vh=-13.1+/-3.4 versus -18.9+/-3.6 mV, P<0.05) without modifying the activation and deactivation kinetics. SP-induced block (1 micromol/L) appeared at the range of membrane potentials coinciding with that of channel activation, and thereafter, it remained constant, reaching 24.7+/-3.8% at +60 mV (n=6, P<0.05). CA (0.01 nmol/L to 500 micromol/L) blocked HERG channels in a voltage- and frequency-independent manner. CA at 1 nmol/L shifted the midpoint of the activation curve to -19.9+/-1.8 mV and accelerated the time course of channel activation (tau=1064+/-125 versus 820+/-93 ms, n=11, P<0.01). The envelope of the tail test demonstrated that at the very beginning of the pulses to +40 mV (25 ms), a certain amount of block was apparent (31.3+/-9.9%). CA did not modify the voltage-dependence of HERG channel inactivation (Vh=-60.8+/-5.6 versus -62.9+/-3.1 mV, n=6, P>0.05) or the kinetics of the reactivation process at any potential tested. CA and aldosterone also blocked the native I(Kr) in guinea-pig ventricular myocytes.


CONCLUSIONS
At concentrations reached after administration of therapeutic doses of SP, CA blocked the HERG channels by binding to both the closed and open states of the channel.
Caballero
Ricardo
R
Department of Pharmacology, School of Medicine, Universidad Complutense, Madrid, Spain.
Moreno
Ignacio
I
González
Teresa
T
Arias
Cristina
C
Valenzuela
Carmen
C
Delpón
Eva
E
Tamargo
Juan
J
D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism; D002191:Canrenoic Acid / Q000494:pharmacology*; D027682:Cation Transport Proteins; D006224:Cricetinae; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D004558:Electric Stimulation; D051638:Ether-A-Go-Go Potassium Channels; D006168:Guinea Pigs; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D013148:Spironolactone / Q000378:metabolism / Q000494:pharmacology*; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014162:Transfection
D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D013148:Spironolactone; D000450:Aldosterone; D002191:Canrenoic Acid