Abstract 2813: Endothelin-1 Increases L-type Ca Current of Rat Ventricular Myocytes via an Activation of Protein Kinase C and Ca/calmodulin Dependent Protein Kinase II
[Introduction] Endothelin-1 (ET-1) shows a positive inotropic effect but the effect of ET-1 on L-type Ca current (ICa) is controversial. The effect appears to depend on patch clamp configuration. We assessed the hypothesis that ET-1 increases ICa via an activation of Ca/calmodulin dependent protein kinase II (CaMKII).
[Methods] The perforated patch clamp technique was used to measure ICa in isolated rat ventricular myocytes. All the experiments were performed at room temperature. Holding potential was set −40 mV and depolarization to 0 mV was applied every 10 s. Protein expression of endothelin receptor subtypes was examined by Western immunoblott analysis.
[Results] ET-1 (10 nM) increased ICa without changing the current-voltage relation. ICa reached steady state 15 min after application of ET-1 when the measurement was done. The increase in ICa by ET-1 was blocked by chelerythrine (5 uM), a protein kinase C (PKC) inhibitor and KN-93 (0.5 uM), a CaMKII inhibitor, but not by KN-92 (0.5 uM), the inactive analogue of KN-93. The increase was blocked by BQ-123 (1uM), a selective ETA antagonist, but not by BQ-788 (1uM), a selective ETB ntagonist (Fig⇓). In Western immunoblott analysis, ETA receptor was found in membrane fraction of rat ventricular myocytes but ETB receptor was not.
[Conclusion] ET-1 increases ICa via ETA-PKC-CaMKII pathway.