Conformational changes of a Ca -binding domain of the Na /Ca exchanger monitored by FRET in transgenic zebrafish heart

Xie Y, Ottolia M, John SA, Chen J, Philipson KD. Conformational changes of a Ca -binding domain of the Na /Ca exchanger monitored by FRET in transgenic zebrafish heart. Am J Physiol Cell Physiol 295: C388–C393, 2008. First published June 11, 2008; doi:10.1152/ajpcell.00178.2008.—The Na /Ca exchanger is the major Ca extrusion mechanism in cardiac myocytes. The activity of the cardiac Na /Ca exchanger is dynamically regulated by intracellular Ca . Previous studies indicate that Ca binding to a high-affinity Ca -binding domain (CBD1) in the large intracellular loop is involved in regulation. We generated transgenic zebrafish with cardiac-specific expression of CBD1 linked to yellow and cyan fluorescent protein. Ca binding to CBD1 induces conformational changes, as detected by fluorescence resonance energy transfer. With this transgenic fish model, we were able to monitor conformational changes of the Ca regulatory domain of Na /Ca exchanger in intact hearts. Treatment with the positive inotropic agents ouabain and isoproterenol increased both Ca transients and Ca -induced changes in fluorescence resonance energy transfer. The results indicate that Ca regulation of the Na /Ca exchanger domain CBD1 changes with inotropic state. The transgenic fish models will be useful to further characterize the regulatory properties of the Na /Ca exchanger in vivo.