Intracellular and extracellular renin have opposite effects on the regulation of heart cell volume. Implications for myocardial ischaemia

摘要

The influence of intracellular renin plus angiotensinogen (Ao) as well as angiotensin (Ang) II on cell volume was investigated in myocytes isolated from the heart of four-month-old cardiomyopathic hamsters (TO-2) and normal hamsters (F1B). Measurements of cell width and cell length were performed on quiescent cells using a Px-it imaging and computer system.The cell volume was calculated assuming the cells as elliptical cylinders and taking the cell depth equal to one third of cell width. For measurements of sodium pump current, the cells were voltage clamped (holding potential -40 mV) using the whole cell configuration. Cells were exposed to K-free solution to inhibit the pump and then to normal Krebs solution to reactivate the pump. In other experiments the cells were voltage clamped (holding potential -40 mV)and changes in the background current elicited by renin plus Ao or by Ang II were monitored. The results indicated that: a) intracellular dialysis of renin (128 pmol Ang I/ml) plus Ao (110 pmol Ang I generated by renin by exhaustion) decreased the cell volume concurrently with the activation of the sodium pump; b) intracellular losartan (10-8 M) or extracellular ouabain (10-8 M) abolished the effect of renin plus Ao on cell volume; c) intracellular Ang II (10-8 M), by itself, reduced cell volume and increased the pump current density; d) extracellular administration of renin plus Ao, at the same concentration used intracellularly, increased cell volume and inhibited the sodium pump. This increase of cell volume elicited by extracellular renin plus Ao was related to the activation of the Na-K-2Cl cotransporter; e) intracellular Ang II (10-8 M) reversed cell swelling induced by hypotonic solutions. Conclusions. Intracellular and extracellular renin plus Ao have opposite effects on sodium pump and cell volume regulation in the failing heart. Both effects of renin plus Ao are dependent upon the formation of Ang II. Since intracellular Ang II counteracted the cell swelling induced by hypotonic solution, it is reasonable to think that the activation of the intracrine renin-angiotensin system might play a protective role during myocardial ischaemia by reducing cell volume.