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(Hypertension. 2006;48:587.)
© 2006 American Heart Association, Inc.

Original Articles

Functional Expression of the TRPM4 Cationic Current in Ventricular Cardiomyocytes From Spontaneously Hypertensive Rats

Romain Guinamard; Marie Demion; Christophe Magaud; Daniel Potreau; Patrick Bois

From the Institut de Physiologie et Biologie Cellulaires, Centre National de la Recherche Scientifique Unité Mixte de Recherche, Université de Poitiers, Poitiers, France.

Correspondence to Romain Guinamard, Centre National de la Recherche Scientifique Unité mixte de recherche 6187, Université de Poitiers, 40 av du Recteur Pineau, 86022 Poitiers Cedex, France. E-mail romain.guinamard{at}univ-poitiers.fr

Cardiac hypertrophy is associated with electrophysiological modifications, including modification of action potential shape that can give rise to arrhythmias. We report here a higher detection of a calcium-activated nonselective cation current in cardiomyocytes of spontaneously hypertensive rats (SHRs), a model of hypertension and heart hypertrophy when compared with Wistar-Kyoto (WKY) rat, its normotensive equivalent. Freshly isolated cells from the left ventricles of 3- to 6-month-old WKY rats or SHRs were used for patch-clamp recordings. In inside-out patches, the channel presented a linear conductance of 25±0.5 pS, did not discriminate Na⁺ over K⁺, and was not permeable to Ca²⁺. Open probability was increased by depolarization and a rise in [Ca²⁺]_i (dissociation constant=10±5.4 µmol/L) but reduced by 0.5 mmol/L [ATP]_i, 10 µmol/L glibenclamide, or flufenamic acid (IC₅₀=5.5±1.7 µmol/L). Thus, it owns the fingerprint of the TRPM4 current. Although rarely detected in WKY cardiomyocytes, the current was present in >50% of patches from SHR cardiomyocytes. Moreover, by performing RT-PCR from ventricular samples, we observed that TRPM4 mRNA detection was higher in SHRs than in WKY rats. We propose that a TRPM4 current is expressed in ventricular cardiomyocytes from SHRs. According to its properties, this channel may contribute to the transient inward current implicated in delayed-after-depolarizations observed during [Ca²⁺] overload of cardiomyocytes.

Key Words: hypertrophy • cation channel • ventricular function

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