Angiotensin II increases L-type Ca²⁺ current in gramicidin D-perforated adult rabbit ventricular myocytes: comparison with conventional patch-clamp method

Abstract.

The effects of angiotensin II (Ang II) on L-type Ca²⁺current (I _Ca,L) remains controversial. We studied the effects of Ang II on I _Ca,L in single adult rabbit ventricular myocytes using a perforated patch-clamp technique with gramicidin D. Ang II increased I _Ca,L in a concentration-dependent manner (EC₅₀=0.75 nM). In contrast, in conventional whole-cell patch-calmp, I _Ca,L ran down gradually and the I _Ca,L response to Ang II was variable, suggesting the potential loss of diffusible components crucial for the Ang II-induced signaling process. An AT₁ antagonist, CV11974 (0.1 µM), completely inhibited the increase in I _Ca,L induced by Ang II (0.1 µM), whereas an AT₂ antagonist, PD123319 (10 µM), did not influence the I _Ca,L increase. Neither pre- nor after-treatment with a Na⁺/H⁺ exchange (NHE) inhibitor HOE642 (1 µM) affected the Ang II-induced increase in I _Ca,L. The protein kinase C (PKC) inhibitor chelerythrine (1 µM) did not affect the Ang II-induced I _Ca,L increase. The present findings indicate that Ang II increases I _Ca,L via AT₁ receptors in adult rabbit ventricular myocytes. Neither the activation of NHE nor PKC may contribute to the Ang II-induced activation of I _Ca,L.