Excitation-contraction coupling in pulmonary vascular smooth muscle involves tyrosine kinase and Rho kinase

Abstract

We investigated the mechanisms that underlie the responses to norepinephrine (NE) and thromboxane (Tx) A(2) (TxA2) in the canine pulmonary vasculature with fura 2 fluorimetric, intracellular microelectrode, and force transduction techniques. KCl, caffeine, and cyclopiazonic acid elevated intracellular Ca2+ concentration levels and tone, indicating that Ca2+ mobilization is sufficient to produce contraction. However, contractions evoked by NE or the TxA2 mimetic U-46619 were unaffected by nifedipine or by omitting external Ca2+ and were reduced only partially by depleting the internal Ca2+ store; furthermore, NE-evoked depolarization was subthreshold for voltage-dependent Ca2+ currents. Agonist-evoked contractions were insensitive to inhibitors of protein kinase C (calphostin C and chelerythrine), mitogen-activated protein kinase kinase (PD-98059), and p38 kinase (SB-203580) but were abolished by the tyrosine kinase inhibitor genistein and the Rho kinase inhibitor Y-27632. We conclude that, although Ca2+ influx and Ca2+ release are sufficient for contraction, they are not necessary for adrenergic or TxA2 contractions. Instead, excitation-contraction coupling involves the activation of tyrosine kinase and Rho kinase, leading to enhanced Ca2+ sensitivity of the contractile apparatus.

Cellular mechanisms of thromboxane A2-mediated contraction in pulmonary veins

“…U-46619 has been shown to constrict human pulmonary veins harvested during lung cancer surgery via activation of TXA 2 -selective prostanoid receptors (35). Only one previous study has investigated intracellular mechanisms that could potentially mediate U-46619 contraction in pulmonary veins (13). The goal of the present study was to investigate the roles of both [Ca 2ϩ ] i and myofilament Ca 2ϩ sensitivity in the contractile response to U-46619 in pulmonary veins.…”

“…The TXA 2 analog, U-46619, is known to cause constriction of pulmonary veins (13). Pulmonary venous constriction can increase pulmonary capillary pressure and transvascular fluid flux to cause pulmonary edema, which can adversely affect blood oxygenation and right ventricular function.…”

“…Agonistinduced vascular smooth muscle contraction is mediated by an increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) and/or an increase in myofilament Ca 2ϩ sensitivity. We are aware of only one study that has investigated the effects of TXA 2 on [Ca 2ϩ ] i in pulmonary veins (13). In that study, changes in tension in response to the TXA 2 analog, U-46619, were measured in pulmonary venous rings, whereas changes in [Ca 2ϩ ] i were measured separately in dispersed pulmonary venous smooth muscle cells (13).…”

“…We are aware of only one study that has investigated the effects of TXA 2 on [Ca 2ϩ ] i in pulmonary veins (13). In that study, changes in tension in response to the TXA 2 analog, U-46619, were measured in pulmonary venous rings, whereas changes in [Ca 2ϩ ] i were measured separately in dispersed pulmonary venous smooth muscle cells (13). Although U-46619 was found to cause marked contraction in pulmonary venous rings, it failed to evoke any change in [Ca 2ϩ ] i in a majority (56%) of the dispersed pulmonary venous smooth muscle cells (13).…”

“…In that study, changes in tension in response to the TXA 2 analog, U-46619, were measured in pulmonary venous rings, whereas changes in [Ca 2ϩ ] i were measured separately in dispersed pulmonary venous smooth muscle cells (13). Although U-46619 was found to cause marked contraction in pulmonary venous rings, it failed to evoke any change in [Ca 2ϩ ] i in a majority (56%) of the dispersed pulmonary venous smooth muscle cells (13). To our knowledge, simultaneous changes in tension and [Ca 2ϩ ] i in response to TXA 2 in pulmonary veins have never been reported.…”