Introduction: 

Mechanisms of AngII-dependent Ca2+ signaling in cells of local renin-angiotensin systems are poorly understood. The retinal pigment epithelium (RPE) forms part of the blood/retina barrier and transduces changes in systemic renin-angiotensin system into changes in the local intra-retinal renin-angiotensin system. In order to analyze the underlying signal transduction mechanism, we studied ion channels activated by AngII in RPE cells.

Methods: 

We used perforated patch recordings from pig RPE cells under extra- and intracellular K+-free conditions at holding potential -40mV which corresponds the resting potential of RPE cells. The cells were electrically stimulated by voltage-ramps between -140mV to +60mV. The concentration of AngII and SKF96365, a Ca2+ channel and possible TRPV2 blocker, are both 100nM. To knock-down TRPV2 channel expression, RPE cells were treated with siRNA.

Results: 

Under resting conditions, the membrane currents from cultured RPE cells showed a reversal potential of -40 mV indicating a resting Cl- conductance under the recording conditions. The application of AngII led to an inward current at -40 mV membrane potential which was accompanied by increased membrane conductance and a shift of the reversal potential from -40 mV to +10mV. This inward current and the shift in the reversal potential were reversed by application of SKF96365. In cells treated with siRNA against TRPV2, AngII also induced an inward current which was, however, insensitive to SKF96365. Cells transfected with scrambled siRNA behaved comparable to non-transfected cells.

Conclusions: 

In summary we conclude that AngII activates at the resting potential of RPE cells an inward current mainly through TRPV2 channels.

Figure 1