Renin-angiotensin system expression and secretory function in cultured human ciliary body non-pigmented epithelium

Background: Renin-angiotensin system (RAS) components have been identified in human ciliary body and aqueous humour, pointing to a role for the RAS in the regulation of aqueous humour dynamics. Here, the authors examine the functional expression of a RAS and the effects of angiotensin 11 (All) on a signal transcluction pathway and ion secretion mechanism in cultured human ciliary body non-pigmented epithelium (HNPE). Methods: RAS expression was examined in cultured HNPE cells using polymerase chain reaction (PCR) analysis. Secretary function was determined using spectrofluorescence imaging microscopy to measure cell calcium (Ca2+) and volume responses. Single channel patch clamp techniques were employed to investigate ion channel activity. Results: PCR analysis demonstrated the expression of angiotensinogen and the AT receptor in HNPE cells. A large conductance potassium (BK) channel (mean 190 (SEM 5.6) pS, n = 22 cells), was observed in plasma membrane patches. This channel was calcium sensitive with channel open probability (Pal increasing with increasing Ca2+, (K-0.5 10.79 (0.44) muM Ca2+, Hill coefficient of 1.04 (0.04)). I All (100 nM) increased the number (N) of active BK channels in HNPE cells and also the probability of channel opening (Po). N.P. increased from 0.008 (0.002) to 1.38 (0.4) following the addition of All (p=0.0064). All also induced a rapid rise in Ca2+, from resting values of 112 (14) nM to a peak of 992 (106) nM (p< 10(-4)). A simultaneous cell volume reduction of 24.70% (3.34%) (p< 10(-4)) occurred during this calcium signal. Losartan (I pM) significantly blocked the All induced BK channel activation 2(p=0.01 3 1), the Ca, response (p< 10(-4)), and the All induced volume effect (p-0.00,46). Conclusion: It was demonstrated that All activates a Ca2+ signalling system which subsequently increases potassium ion channel activity. These effects are accompanied simultaneously by cell volume loss, indicating that All acts as receptor operated secretagogue in HNPE cells. The ability of an AT, receptor antagonist to inhibit these processes may thus offer a new family of pharmaceutical agents to the current ormamentarium in the treatment of glaucoma.