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

The effects of angiotensin II (Ang II) on L-type Ca(2+)current (I-Ca,I-L) remains controversial. We studied the effects of Ang II on I-Ca,I-L in single adult rabbit ventricular myocytes using a perforated patch-clamp technique with gramicidin D. Ang II increased I-Ca,I-L in a concentration-dependent manner (EC50 = 0.75 nM). In contrast, in conventional whole-cell patch-calmp, I-Ca,I-L ran down gradually and the I-Ca,I-L response to Ang II was variable, suggesting the potential loss of diffusible components crucial for the Ang II-induced signaling process. An AT(1) antagonist, CV11974 (0.1 muM), completely inhibited the increase in I-Ca,I-L induced by Ang II (0.1 muM), whereas an AT(2) antagonist, PD123319 (10 muM), did not influence the I-Ca,I-L increase. Neither pre- nor after-treatment with a Na+/H+ exchange (NHE) inhibitor HOE642 (1 muM) affected the Ang II-induced increase in I-Ca,I-L. The protein kinase C (PKC) inhibitor chelerythrine (1 muM) did not affect the Ang II-induced I-Ca,I-L increase. The present findings indicate that Ang II increases I-Ca,I-L via AT, receptors in adult rabbit ventricular myocytes. Neither the activation of NHE nor PKC may contribute to the Ang I-induced activation of I-Ca,I-L.