Acute, pro‐contractile effects of prorenin on rat mesenteric arteries

Prorenin and the prorenin receptor ((P)RR) are important, yet controversial, members of the renin–angiotensin–aldosterone system. The ((P)RR) is expressed throughout the body, including the vasculature, however, the direct effect of prorenin on arterial contractility is yet to be determined. Within rat mesenteric arteries, immunostaining and proximity ligation assays were used to determine the interacting partners of (P)RR in freshly isolated vascular smooth muscle cells (VSMCs). Wire myography examined the functional effect of prorenin. Simultaneous changes in [Ca ²⁺] _i and force were recorded in arteries loaded with Fura-2AM. Spontaneously transient outward currents were recorded via perforated whole-cell patch-clamp configuration in freshly isolated VSMCs. We found that the (P)RR is located within a distance of less than 40 nm from the V-ATPase, caveolin-1, ryanodine receptors, and large conductance Ca ²⁺-activated K ⁺ channels (BK _Ca) in VSMCs. [Ca ²⁺] _i imaging and isometric tension recordings indicate that 1 nM prorenin enhanced α1-adrenoreceptor-mediated contraction, associated with an increased number of Ca ²⁺ waves, independent of voltage-gated Ca ²⁺ channels activation. Incubation of VSMCs with 1 nM prorenin decreased the amplitude and frequency of spontaneously transient outward currents and attenuated BK _Ca-mediated relaxation. Inhibition of the V-ATPase with 100 nM bafilomycin prevented prorenin-mediated inhibition of BK _Ca-derived relaxation. Renin (1 nM) had no effect on BK _Ca-mediated relaxation. In conclusion, prorenin enhances arterial contractility by inhibition of BK _Ca and increasing intracellular Ca ²⁺ release. It is likely that this effect is mediated through a local shift in pH upon activation of the (P)RR and stimulation of the V-ATPase.