Electrophysiologic effects of the IK1 inhibitor PA-6 are modulated by extracellular potassium in isolated guinea pig hearts

TY - JOUR

T1 - Electrophysiologic effects of the IK1 inhibitor PA-6 are modulated by extracellular potassium in isolated guinea pig hearts

AU - Hoeker, Gregory S

AU - Skarsfeldt, Mark A

AU - Jespersen, Thomas

AU - Poelzing, Steven

N1 - © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.

PY - 2017/1/1

Y1 - 2017/1/1

N2 - The pentamidine analog PA-6 was developed as a specific inward rectifier potassium current (IK 1) antagonist, because established inhibitors either lack specificity or have side effects that prohibit their use in vivo. We previously demonstrated that BaCl2, an established IK 1 inhibitor, could prolong action potential duration (APD) and increase cardiac conduction velocity (CV). However, few studies have addressed whether targeted IK 1 inhibition similarly affects ventricular electrophysiology. The aim of this study was to determine the effects of PA-6 on cardiac repolarization and conduction in Langendorff-perfused guinea pig hearts. PA-6 (200 nm) or vehicle was perfused into ex-vivo guinea pig hearts for 60 min. Hearts were optically mapped with di-4-ANEPPS to quantify CV and APD at 90% repolarization (APD90). Ventricular APD90 was significantly prolonged in hearts treated with PA-6 (115 ± 2% of baseline; P < 0.05), but not vehicle (105 ± 2% of baseline). PA-6 slightly, but significantly, increased transverse CV by 7%. PA-6 significantly prolonged APD90 during hypokalemia (2 mmol/L [K+]o), although to a lesser degree than observed at 4.56 mmol/L [K+]o. In contrast, the effect of PA-6 on CV was more pronounced during hypokalemia, where transverse CV with PA-6 (24 ± 2 cm/sec) was significantly faster than with vehicle (13 ± 3 cm/sec, P < 0.05). These results show that under normokalemic conditions, PA-6 significantly prolonged APD90, whereas its effect on CV was modest. During hypokalemia, PA-6 prolonged APD90 to a lesser degree, but profoundly increased CV. Thus, in intact guinea pig hearts, the electrophysiologic effects of the IK 1 inhibitor, PA-6, are [K+]o-dependent.

AB - The pentamidine analog PA-6 was developed as a specific inward rectifier potassium current (IK 1) antagonist, because established inhibitors either lack specificity or have side effects that prohibit their use in vivo. We previously demonstrated that BaCl2, an established IK 1 inhibitor, could prolong action potential duration (APD) and increase cardiac conduction velocity (CV). However, few studies have addressed whether targeted IK 1 inhibition similarly affects ventricular electrophysiology. The aim of this study was to determine the effects of PA-6 on cardiac repolarization and conduction in Langendorff-perfused guinea pig hearts. PA-6 (200 nm) or vehicle was perfused into ex-vivo guinea pig hearts for 60 min. Hearts were optically mapped with di-4-ANEPPS to quantify CV and APD at 90% repolarization (APD90). Ventricular APD90 was significantly prolonged in hearts treated with PA-6 (115 ± 2% of baseline; P < 0.05), but not vehicle (105 ± 2% of baseline). PA-6 slightly, but significantly, increased transverse CV by 7%. PA-6 significantly prolonged APD90 during hypokalemia (2 mmol/L [K+]o), although to a lesser degree than observed at 4.56 mmol/L [K+]o. In contrast, the effect of PA-6 on CV was more pronounced during hypokalemia, where transverse CV with PA-6 (24 ± 2 cm/sec) was significantly faster than with vehicle (13 ± 3 cm/sec, P < 0.05). These results show that under normokalemic conditions, PA-6 significantly prolonged APD90, whereas its effect on CV was modest. During hypokalemia, PA-6 prolonged APD90 to a lesser degree, but profoundly increased CV. Thus, in intact guinea pig hearts, the electrophysiologic effects of the IK 1 inhibitor, PA-6, are [K+]o-dependent.

KW - Action Potentials/drug effects

KW - Animals

KW - Anthraquinones/administration & dosage

KW - Barium Compounds/administration & dosage

KW - Chlorides/administration & dosage

KW - Electrophysiological Phenomena

KW - Guinea Pigs

KW - Heart/physiology

KW - Heart Conduction System/drug effects

KW - Heart Ventricles/drug effects

KW - Hypokalemia/physiopathology

KW - Male

KW - Pentamidine/analogs & derivatives

KW - Potassium/metabolism

KW - Potassium Channel Blockers/administration & dosage

KW - Potassium Channels/drug effects

KW - Pyridinium Compounds/analysis

KW - Voltage-Sensitive Dye Imaging/methods

U2 - 10.14814/phy2.13120

DO - 10.14814/phy2.13120

M3 - Journal article

C2 - 28087819

SN - 2051-817X

VL - 5

JO - Physiological Reports

JF - Physiological Reports

IS - 1

M1 - e13120

ER -