Intracellular Ca²⁺ oscillations in vascular smooth muscle cells

We monitored caffeine- and histamine-induced [Ca²⁺](i) oscillations by patch-clamp whole cell recordings of K(Ca)-current in single smooth muscle cells of rabbit cerebral (basilar) artery. Superfusion of caffeine (1 mM) or histamine (1-3 μM) induced periodic oscillations of large whole-cell K- current with fairly uniform amplitudes and intervals. Repetitive activations of the large-conductance K(Ca)-channels were recorded in the cell-attached patch mode. Inclusion of heparin (3 mg/ml) in the pipette solution failed to inhibit the oscillation caused by caffeine treatment, but blocked histamine- evoked oscillations. Ryanodine (1-10 μM) abolished both caffeine and histamine-induced oscillations. Removal of extracellular Ca²⁺, but not verapamil or Cd²⁺, abolished the caffeine-induced oscillations, and the changes in the oscillatory frequency closely reflected the altered Ca²⁺ influx rate. These results indicate that in smooth muscle cells of the rabbit cerebral artery, ryanodine sensitive Ca²⁺-induced Ca²⁺ release (CICR) pools play key roles for the generation of the [Ca²⁺](i) oscillations.