Intravenous anesthetics inhibit capacitative calcium entry in pulmonary venous smooth muscle cells.

Background: The authors have previously demonstrated that propofol attenuates capacitative calcium entry (CCE) via the protein kinase C signaling pathway in pulmonary artery smooth muscle cells (PVSMCs). The current goals were to determine whether CCE exists in PVSMCs; to assess the roles of the protein kinase C, tyrosine kinase (TK), and rho-kinase signaling pathways in regulating CCE; and to investigate the extent and cellular mechanisms by which intravenous anesthetics (thiopental, midazolam, ketamine, and propofol) alter CCE.

Methods: Primary cultures of fura-2-loaded canine PVSMCs were placed in a dish (37 degrees C) on an inverted fluorescence microscope. Intracellular Ca2+ concentration ([Ca2+]i) was measured as the 340/380 fluorescence ratio in individual PVSMCs. 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).

Results: Thapsigargin caused a transient increase in [Ca2+]i (160 +/- 6%). Restoring extracellular Ca2+ caused a rapid peak increase in [Ca2+]i (155 +/- 7% of baseline), followed by a sustained increase in [Ca2+]i (129 +/- 5% of baseline), i.e., CCE was stimulated in PVSMCs. Neither protein kinase C activation nor inhibition had an effect on CCE. rho-Kinase inhibition also had no effect on CCE, whereas TK inhibition attenuated both peak and sustained CCE. Thiopental, midazolam, ketamine, and propofol each attenuated both peak and sustained CCE. TK inhibition abolished the thiopental-, midazolam-, and ketamine-induced, but not the propofol-induced, decreases in CCE.

Conclusion: Capacitative calcium entry is present in canine PVSMCs. Thiopental, midazolam, and ketamine attenuate CCE primarily via the TK signaling pathway. Propofol attenuates CCE via a TK-independent mechanism.