Propofol attenuates capacitative calcium entry in pulmonary artery smooth muscle cells

Abstract

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°C) on an inverted fluorescence microscope. Intracellular Ca2+ concentration was measured using fura 2 in PASMCs using a dual-wavelength spectrofluorometer. Thapsigargin (1 μM), 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 μM) attenuated CCE in a dose-dependent manner (peak: 85 ± 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.