Angiotensin II (AngII) constricts isolated descending vasa recta (DVR), apparently by contracting surrounding pericytes, at least partly by activating transient or steady inward chloride currents (Pallone & Huang, 2002; Zhang et al. 2001). In smooth muscle, transient chloride currents depend upon Ca²⁺ release from intracellular stores and diminish when stores are depleted by agonists (Large & Wang, 1996). Some intracellular Ca²⁺ stores respond to inositol 1,4,5-triphosphate (IP₃) or cyclopiazonic acid (CPA) and some to ryanodine or caffeine. IP₃– and ryanodine-sensitive stores may overlap or be separate, in different types of vascular smooth muscle (Janiak et al. 2001). This study examines the effects of CPA or caffeine upon transient inward currents in pericytes clamped at -50 mV, during whole-cell permeabilised patch-clamp recording from isolated DVR exposed to AngII.

Individual DVR were dissected from renal tissue kept at 4 °C (Pallone & Huang, 2002; Zhang et al. 2001), after removal from rats humanely killed by stunning and cervical dislocation. DVR were incubated in collagenase and hyaluronidase (0.4 mg ml^-1 of each) at room temperature for 8-9 min, stored on ice and transferred at intervals to solution at room temperature, containing (mM): Na⁺ 150, K⁺ 5, Mg²⁺ 1, Ca²⁺ 1, Cl^– 159, Hepes 10 and glucose 10, plus 18β-glycyrrhetinic acid (40 µM), a gap junction blocker (Yamamoto et al. 1998). Heat-polished pipettes containing a solution of (mM): Na⁺ 10, K⁺ 140, Cl^– 150 and Hepes 10, plus gramicidin (0.4 mg ml^-1), were applied to pericytes to form gigaohm seals.

CPA significantly reduced the mean frequency of these transient currents (Fig. 1), but caffeine did not, which suggests that pericytes on DVR contain heterogeneous Ca²⁺ stores. Caffeine significantly increased mean current amplitude, by an unknown mechanism.

This work was supported by British Heart Foundation grant PG/2000105.