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 authors aimed to investigate the effects of propofol on CCE and to assess the extent 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 of canine intrapulmonary artery. Fura 2-loaded PASMCs were placed in a dish (37 degrees C) on an inverted fluorescence microscope. Intracellular Ca2+ concentration was measured using fura 2 in PASMCs using a dual-wavelength spectrofluorometer. Thapsigargin (1 microM), a sarcoplasmic reticulum Ca2+-adenosine triphosphatase inhibitor, was used to deplete intracellular Ca2+ stores after removing extracellular Ca2+. CCE was activated when extracellular Ca2+ (2.2 mM) was restored. RESULTS: Thapsigargin caused a transient increase in intracellular Ca2+ concentration (182+/-11%). Restoring extracellular calcium (to induce CCE) resulted in a peak (246+/-12% of baseline) and a sustained (187+/-7% of baseline) increase in intracellular Ca2+ concentration. Propofol (1, 10, 100 microM) attenuated CCE in a dose-dependent manner (peak: 85+/-3, 70+/-4, 62+/-4%; sustained: 94+/-5, 80+/-5, 72+/-5% of control respectively). Tyrosine kinase inhibition (tyrphostin 23) attenuated CCE (peak: 67+/-4%; sustained: 74+/-5% of control), but the propofol-induced decrease in CCE was still apparent after tyrosine kinases inhibition. PKC activation (phorbol 12-myristate 13-acetate) attenuated CCE (peak: 48+/-1%; sustained: 53+/-3% of control), whereas PKC inhibition (bisindolylmaleimide) potentiated 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. Propofol attenuates CCE primarily via a PKC-dependent pathway. CCE should be considered a possible cellular target for anesthetic agents that alter vascular smooth muscle tone.