Impaired endocytosis of the ion channel TRPM4 is associated with human progressive familial heart block type I
Martin Kruse, … , Paul Brink, Olaf Pongs
Martin Kruse, … , Paul Brink, Olaf Pongs
Published August 24, 2009
Citation Information: J Clin Invest. 2009;119(9):2737-2744. https://doi.org/10.1172/JCI38292.
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Research Article

Impaired endocytosis of the ion channel TRPM4 is associated with human progressive familial heart block type I

Abstract

Progressive familial heart block type I (PFHBI) is a progressive cardiac bundle branch disease in the His-Purkinje system that exhibits autosomal-dominant inheritance. In 3 branches of a large South African Afrikaner pedigree with an autosomal-dominant form of PFHBI, we identified the mutation c.19G→A in the transient receptor potential cation channel, subfamily M, member 4 gene (TRPM4) at chromosomal locus 19q13.3. This mutation predicted the amino acid substitution p.E7K in the TRPM4 amino terminus. TRPM4 encodes a Ca2+-activated nonselective cation (CAN) channel that belongs to the transient receptor potential melastatin ion channel family. Quantitative analysis of TRPM4 mRNA content in human cardiac tissue showed the highest expression level in Purkinje fibers. Cellular expression studies showed that the c.19G→A missense mutation attenuated deSUMOylation of the TRPM4 channel. The resulting constitutive SUMOylation of the mutant TRPM4 channel impaired endocytosis and led to elevated TRPM4 channel density at the cell surface. Our data therefore revealed a gain-of-function mechanism underlying this type of familial heart block.

Authors

Martin Kruse, Eric Schulze-Bahr, Valerie Corfield, Alf Beckmann, Birgit Stallmeyer, Güven Kurtbay, Iris Ohmert, Ellen Schulze-Bahr, Paul Brink, Olaf Pongs

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Figure 3

Expression of human TRPM4 and TRPM4E7K in HEK 293 cells.

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Expression of human TRPM4 and TRPM4E7K in HEK 293 cells. Unless othe...
Unless otherwise indicated, black traces denote TRPM4; red traces denote TRPM4E7K. (A) Normalized current-voltage relationship for TRPM4 and TRPM4E7K obtained from 250-ms voltage ramps measured in the whole-cell patch-clamp configuration from –120 to +100 mV. Holding potential was –60 mV. (B) Ca2+ dependence of TRPM4 current densities (I/Imax) obtained from voltage ramps measured at –80 and +80 mV (n = 7–16). [Ca2+]i, intracellular Ca2+. (C) AMP-PNP block of WT TRPM4 and TRPM4E7K current. Holding potential was 0 mV. Currents, elicited by a 250-ms pulse to +100 mV after a 500-ms pulse to –100 mV, were recorded before (0; black) and after application of 500 μM AMP-PNP (0.5; red) Scale bars: 200 ms, 0.5 nA. (D) Normalized current densities (I/Inorm) of TRPM4E7K expressed alone (n = 13) or in a 1:1 ratio with TRPM4 (WT/E7K, n = 6) obtained from voltage ramps measured at +40 and +80 mV. n = 16 (WT TRPM4). *P < 0.05 versus WT. (E) Single-channel currents recorded from inside-out patches at –100 mV. Scale bars: 1 s, 5 pA. (F) Histogram plots of TRPM4 and TRPM4E7K traces shown in E. (G) Po of TRPM4 and TRPM4E7K channel at +100 mV (n = 8–9).