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 microM) 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 oscillations caused by caffeine treatment, but blocked histamine-evoked oscillations. Ryanodine (1-10 microM) 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 Ca(2+)-induced Ca2+ release (CICR) pools play key roles for the generation of the [Ca2+]i oscillations.