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(Circulation. 1997;96:1266-1274.)
© 1997 American Heart Association, Inc.

Articles

Regional Alteration of the Transient Outward Current in Human Left Ventricular Septum During Compensated Hypertrophy

Patrick Bailly, MD; Jean-Pierre Bénitah, PhD; Maud Mouchonière, PhD; Guy Vassort, DSc; ; Paco Lorente, MD

From the Département de Chirurgie Cardiovasculaire, Hôpital Gabriel Montpied, Clermont-Ferrand (P.B.), and U 390 INSERM, CHU Arnaud de Villeneuve, Montpellier (G.V., P.L.), France. J.-P.B. is currently a postdoctoral fellow in the Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Md. M.M. is currently a postdoctoral fellow in the Institut National de Recherche Agronomique, Theix, France.

Correspondence to Dr Paco Lorente, U 390 INSERM, CHU Arnaud de Villeneuve, 34295 Montpellier, France. E-mail paco{at}u390.montp.inserm.fr

Background A large calcium-insensitive transient outward current (I_to) has been recorded in atria, left ventricular (LV) free wall, and right ventricular septal subendocardium of the human heart. Recent studies suggested a major contribution of this current to the electrical heterogeneity of the heart. However, no data have been reported on the distribution of I_to density within the LV septal wall from compensated human LV hypertrophy.

Methods and Results Microelectrode and patch-clamp techniques were used to record action potentials and I_to in myocytes isolated from superficial (<3 mm deep) and deep (3 to 6 mm deep) layers of LV septum from patients with aortic stenosis and compensated LV hypertrophy. Subendocardial specimens were also obtained from undiseased donor hearts. In none of the superficial subendocardial cells from diseased hearts was a macroscopic I_to recorded (n=42), whereas in cells from the same location from donor hearts, a typical I_to was clearly present, with a peak density of 5.88±0.78 pA/pF at +60 mV (n=4). However, in deep layers from patients with compensated LV hypertrophy, macroscopic I_to was present, with a peak density of 10.50±2.58 pA/pF at +60 mV (n=4). The absence of I_to in superficial septal cells from hypertrophied hearts was not due to a divalent cation–related shift of the current kinetics. Instead, extracellular Ca²⁺ removal induced an I_to-like current, possibly carried by K⁺ ions, with a peak density of 30.7±2.6 pA/pF at +60 mV (n=29). However, its magnitude, kinetics, and pharmacological characteristics did not allow identification of this current as the usual I_to.

Conclusions Both topography and pathology can be major modulating factors of the regional distribution of I_to density in human LV septum. Therefore, they may play a prominent role in determining electrical gradients within this region from which the early depolarization vectors start and the left-to-right activation sequence of the interventricular septum proceeds.

Key Words: action potentials • electrophysiology • hypertrophy • ventricles

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