Chronic in vivo angiotensin II administration differentially modulates the slow delayed rectifier channels in atrial and ventricular myocytes.

BACKGROUND: In the heart, slow delayed rectifier channels provide outward currents (IKs) for action potential (AP) repolarization in a region- and context-dependent manner. In diseased hearts, chronic elevation of angiotensin II (Ang II) may remodel IKs in a region-dependent manner, contributing to atrial and ventricular arrhythmias of different mechanisms.
OBJECTIVE: The purpose of this study was to study whether/how chronic in vivo Ang II administration remodels IKs in atrial and ventricular myocytes.
METHODS: We used the guinea pig (GP) model whose myocytes express robust IKs. GPs were implanted with minipumps containing Ang II or vehicle. Treatment continued for 4-6 weeks. We used patch clamp, immunofluorescence/confocal microscopy, and immunoblots to evaluate changes in IKs function and to explore the underlying mechanisms.
RESULTS: We confirmed the pathologic state of the heart after chronic Ang II treatment. IKs density was increased in atrial myocytes but decreased in ventricular myocytes in Ang II- vs vehicle-treated animals. The former was correlated with an increase in KCNQ1/KCNE1 colocalization in myocyte periphery, whereas the latter was correlated with a decrease in KCNQ1 protein level. Interestingly, these changes in IKs were not translated into expected alterations in AP duration or plateau voltage, indicating that other currents were involved. In atrial myocytes from Ang II-treated animals, the L-type Ca channel current was increased, contributing to AP plateau elevation and AP duration prolongation.
CONCLUSION: IKs is differentially modulated by chronic in vivo Ang II administration between atrial and ventricular myocytes. Other currents remodeled by Ang II treatment also contribute to changes in action potentials.