EXTRACELLULAR ATP INCREASES CYTOSOLIC CALCIUM IN CULTURED RAT RENAL ARTERIAL SMOOTH MUSCLE CELLS

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Abstract
1. Experiments were conducted on cultured renal arterial smooth muscle cells to determine the ability of extracellular ATP to alter cytosolic calcium concentration and to determine the mechanisms by which this effect occurs. 2. ATP (100 μmol/L) caused the fluorescence ratio of fura‐2 to increase from a control value of 1.06±0.05 to 2.06±0.13 (Pn= 8; Pn= 5). Furthermore, the initial increase in fluorescence ratio rapidly declined to 1.02±0.06, indicating that an influx of extracellular calcium is required to sustain the increase in fura‐2 fluorescence. 4. Depletion of intracellular calcium pools with thapsigargin prevented the increase in fura‐2 fluorescence evoked by ATP. 5. These data suggest that ATP‐mediated increases in cytosolic calcium in cultured renal arterial smooth muscle cells involve calcium release from the thapsigargin‐sensitive, intracellular pool in conjunction with calcium influx from the extracellular medium.