Differential effects of intravenous anesthetics on capacitative calcium entry in human pulmonary artery smooth muscle cells

We assessed the roles of the protein kinase C (PKC) and the tyrosine kinase (TK) signaling pathways in regulating capacitative calcium entry (CCE) in human pulmonary artery smooth muscle cells (PASMCs) and investigated the effects of intravenous anesthetics (midazolam, propofol, thiopental, ketamine, etomidate, morphine, and fentanyl) on CCE in human PASMCs. Fura-2-loaded human PASMCs were placed in a dish (37°C) on an inverted fluorescence microscope. Intracellular Ca²⁺ concentration ([Ca²⁺]_i) was measured as the 340/380 fluorescence ratio in individual PASMCs. Thapsigargin, a sarcoplasmic reticulum Ca²⁺-adenosine triphosphatase inhibitor, was used to deplete intracellular Ca²⁺ stores after removing extracellular Ca²⁺. CCE was then activated by restoring extracellular Ca²⁺ (2.2 mM). The effects of PKC activation and inhibition, TK inhibition, and the intravenous anesthetics on CCE were assessed. Thapsigargin caused a transient increase in [Ca²⁺]_i Restoring extracellular Ca²⁺ caused a rapid peak increase in [Ca ²⁺]_i, followed by a sustained increase in [Ca ²⁺]_i; i.e., CCE was stimulated in human PASMCs. PKC activation attenuated (P < 0.05), whereas PKC inhibition potentiated (P < 0.05), both peak and sustained CCE. TK inhibition attenuated (P < 0.05) both peak and sustained CCE. Midazolam, propofol, and thiopental each attenuated (P < 0.05) both peak and sustained CCE, whereas ketamine, etomidate, morphine, and fentanyl had no effect on CCE. Our results suggest that CCE in human PASMCs is influenced by both the TK and PKC signaling pathways. Midazolam, propofol, and thiopental each attenuated CCE, whereas ketamine, etomidate, morphine, and fentanyl had no effect on CCE.