Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC31
Electrophysiological properties and calcium handling in the atrium in mice with cardiac specific deletion of plasma membrane calcium ATPase isoforms 1 (PMCA1)
Y. Wang1, T. Mohamed1, M. Shaheen1, N. Ludwig1, E. Cartwright1, M. Lei1
1. School of Biomedicine, University of Manchester, Manchester, United Kingdom.
The regulation of intracellular Ca2+ plays a crucial role in maintaining normal cardiac function. It is generally thought that plasma membrane calcium ATPase (PMCA) plays a relative modest role in extrusion of Ca2+ from the cytosol comparing with SERCA and Na-Ca exchanger (NCX) (Brini, 2009). However, recent studies have shown that both PMCA 1 and 4 play critical roles for modulating cardiac contractility, hypertrophy, intracellular signalling pathways, calcium homeostasis and vascular tone (Brini & Carafoli, 2009; Cartwright et al., 2009). The role of PMCA1 in atrium electrical function and intracellular Ca2+ regulation, however, has not been previous explored. In the present study, we characterized the electrophysiological properties and calcium handling in the atrium in mice with cardiac specific deletion of plasma membrane calcium ATPase isoforms 1 (PMCA1cko). Mice at 3-4 months old were used for the study. The expression and cellular distribution of PMCA proteins were characterized by Western blotting and immunostaining. Conventional ex vivo isolated Langendorff-perfused heart preparations were used for ECG, monophasic action potential (MAP) and multi-electrode array recordings of extracellular potentials (ECPs) in both control and PMCA1cko mice. The electrophysiological properties and intracellular calcium handing were investigated by isolated atrial cardiac myocytes with whole cell patch clamping. Immunostaining indicated PMCA1 localized at cell membrane and caveolae in control mice. Both Western blotting and immunostaining demonstrated an efficient deletion of PMCA1 protein in atrial myocytes in PMCA1cko mice. PMCA1cko hearts were susceptible to atrial arrhythmias including atrial tachycardia (AT) and atrial fibrillation when given electrical program stimulation, 6 out of 6 PMCA1cko mice examined developed AT/AF compared to 0 out of 5 control mice examined. Single cell study indicates the L-type Ca2+ channel current was reduced approximately 20% in PMCA1cko mice compare with control mice (control n=23, PMCA1cko n=9). There was no significant difference in SR content and current amplitude of NCX (control n=11, PMCA1cko n=15), however, the NCX current decay was prolonged by approximately 40%. Increase external Ca2+ concentration from 1 mM to 2 mM, action potential alternans, early after depolarisation (EAD), delayed after depolarisation (DAD) as well as spontaneous Ca2+ wave were frequently seen in PMCA1cko myocytes. In conclusion, PMCA1 may play a role in maintaining atrial electrical function and intracellular Ca2+ homeostasis, particularly, under stress condition.
Where applicable, experiments conform with Society ethical requirements