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Is an Intracellular Renin–Angiotensin System Involved in Control of Cell Communication in Heart?

Summary: The possible influence of an intracellular renin–angiotensin system (RAS) on control of cell communication in heart muscle was investigated in cell pairs isolated from adult rats. Junctional conductance (gj) was measured with two separated voltage-clamp circuits. Intracellular dialysis of angiotensin I (AI 10−8M) caused a decrease in gj of 76% (SE ± 3.4) (p < 0.05) in 7 min. The effect of AI appears to be due mainly to its conversion to AII because enalaprilat (10−9M) dialysed into the cell caused an appreciable reduction in the effect of AI. AII (10−8M) alone caused a decrease in gj of 60% (SE ± 3.8) (p < 0.05) in 45 s. The effect of AII on gj was suppressed by previous inhibition of protein kinase C (PKC), but enalaprilat could not alter the effect of the peptide. The results indicate that synthesis of AII inside cardiac myocytes plays an important role in modulation of gj and consequently on propagation of the electrical impulse in heart. The effect of AII on gj was blocked by DuP-753 (10−9M) administered intracellularly, whereas (Sar1Val5AlA8) AII also caused a slight decrease (1.97 ± 0.07%) in gj. These findings indicate that an intracellular receptor is involved in the effect of the peptide on gj.