Atrioventricular Node Dysfunction and Ion Channel Transcriptome in Pulmonary Hypertension

Ian P Temple, Sunil Jit R J Logantha, Mais Absi, Yu Zhang, Eleftheria Pervolaraki, Joseph Yanni, Andrew Atkinson, Maria Petkova, Gillian M Quigley, Simon Castro, Mark Drinkhill, Heiko Schneider, Oliver Monfredi, Elizabeth Cartwright, Min Zi, Tomoko T Yamanushi, Vaikom S Mahadevan, Alison M Gurney, Ed White, Henggui Zhang, George Hart, Mark R Boyett, Halina Dobrzynski

Heart block is associated with pulmonary hypertension, and the aim of the study was to test the hypothesis that the heart block is the result of a change in the ion channel transcriptome of the atrioventricular (AV) node. The most commonly used animal model of pulmonary hypertension, the monocrotaline-injected rat, was used. The functional consequences of monocrotaline injection were determined by echocardiography, ECG recording, and electrophysiological experiments on the Langendorff-perfused heart and isolated AV node. The ion channel transcriptome was measured by quantitative PCR, and biophysically detailed computer modeling was used to explore the changes observed. After monocrotaline injection, echocardiography revealed the pattern of pulmonary artery blood flow characteristic of pulmonary hypertension and right-sided hypertrophy and failure; the Langendorff-perfused heart and isolated AV node revealed dysfunction of the AV node (eg, 50% incidence of heart block in isolated AV node); and quantitative PCR revealed a widespread downregulation of ion channel and related genes in the AV node (eg, >50% downregulation of Cav1.2/3 and HCN1/2/4 channels). Computer modeling predicted that the changes in the transcriptome if translated into protein and function would result in heart block. Pulmonary hypertension results in a derangement of the ion channel transcriptome in the AV node, and this is the likely cause of AV node dysfunction in this disease.