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

We investigated the mechanisms that underlie the responses to norepinephrin e (NE) and thromboxane (Tx) A(2) (TxA(2))in the canine pulmonary vasculatur e with fura 2 fluorimetric, intracellular microelectrode, and force transdu ction techniques. KCl, caffeine, and cyclopiazonic acid elevated intracellu lar Ca2+ concentration levels and tone, indicating that Ca2+ mobilization i s sufficient to produce contraction. However, contractions evoked by NE or the TxA(2) mimetic U-46619 were unaffected by nifedipine or by omitting ext ernal Ca2+ and were reduced only partially by depleting the internal Ca2+ s tore; furthermore, NE-evoked depolarization was subthreshold for voltage-de pendent Ca2+ currents. Agonist-evoked contractions were insensitive to inhi bitors of protein kinase C (calphostin C and chelerythrine), mitogen-activa ted protein kinase kinase (PD-98059), and p38 kinase (SB-203580) but were a bolished by the tyrosine kinase inhibitor genistein and the Rho kinase inhi bitor Y-27632. We conclude that, although Ca2+ influx and Ca2+ release are sufficient for contraction, they are not necessary for adrenergic or TxA(2) contractions. Instead, excitation-contraction coupling involves the activa tion of tyrosine kinase and Rho kinase, leading to enhanced Ca2+ sensitivit y of the contractile apparatus.