Video imaging of single, fura2-loaded vascular smooth muscle cells was used to examine the spatial and temporal alterations in calcium, Ca2+, in response to low levels of vasoconstrictor stimuli. 2. Histamine (0.5 mumol/L) produced repetitive oscillations in Ca2+, which appeared to show some variation in amplitude and frequency between cells. 3. Individual oscillations consisted of an initial increase in Ca2+ in a localized region followed by a wave-like propagation of this region of elevated Ca2+ throughout the rest of the cell cytoplasm. 4. It is suggested that the subcellular spatial organization of Ca2+ that was observed during a Ca2+ oscillation allows a population of cells to operate in unison. Thus, oscillatory fluctuations in Ca2+ may contribute to myogenic tone.
