Propofol attenuates capacitative calcium entry in pulmonary artery smooth muscle cells

Background: Depletion of intracellular Ca2+ stores results in capacitative Ca2+ entry (CCE) in pulmonary artery smooth muscle cells (PASMCs). The auth ors aimed to investigate the effects of propofol on CCE and to assess the e xtent to which protein kinase C (PKC) and tyrosine kinases mediate propofol -induced changes in CCE. Methods. Pulmonary artery smooth muscle cells were cultured from explants o f canine intrapulmonary artery. Fura 2-loaded PASMCs were placed in a dish (37 degreesC) on an inverted fluorescence microscope. Intracellular Ca2+ co ncentration was measured using fura 2 in PASMCs using a dual-wavelength spe ctrofluorometer. Thapsigargin (1 mum), a sarcoplasmic reticulum Ca2+-adenos ine triphosphatase inhibitor, was used to deplete intracellular Ca2+ stores after removing extracellular Ca2+. CCE was activated when extracellular Ca 2+ (2.2 mm) was restored. Results. Thapsigargin caused a transient increase In intracellular Ca" conc entration (182 +/- 11%). Restoring extracellular calcium (to induce CCE) re sulted in a peak (246 +/- 12% of baseline) and a sustained (187 +/- 7% of b aseline) increase in intracellular Ca2+ concentration. Propofol (1, 10, 100 mum) attenuated CCE in a do-se-dependent manner (peak: 85 +/- 3, 70 +/- 4, 62 +/- 4%; sustained: 94 +/- 5, 80 +/- 5, 72 +/- 5% of control, respective ly). Tyrosine kinase inhibition (tyrphostin 23) attenuated CCE (peak: 67 +/ - 4%; sustained: 74 +/- 5% of control), but the propofol-induced decrease i n CCE was still apparent after tyrosine kinases inhibition. PKC activation (phorbol 12-myristate 13-acetate) attenuated CCE (peak: 48 +/- 1%; sustaine d: 53 +/- 3% of control), whereas PKC inhibition (bisindolylmaleimide) pote ntiated CCE (peak: 132 +/- 11%; sustained: 120 +/- 4% of control). Moreover , PKC inhibition abolished the propofol-induced attenuation of CCE. Conclusion: Tyrosine kinases activate and PKC inhibits CCE in PASMCs. Propo fol attenuates CCE primarily via a PKC-dependent pathway. CCE should be con sidered a possible cellular target for anesthetic agents that alter vascula r smooth muscle tone.