In CA of both age groups, U-0126 eliminated the PDBu-induced increases of phosphorylated ERK1 and ERK2, whereas total protein levels were unaffected (data not shown; see Ref.19). Furthermore, in adult CA, PDBu led to increased phosphorylation of ERK1, but not ERK2; in fetal CA, the reverse was the case. PDBu-stimulated ERK2 phosphorylation also was significantly greater in FH than FN CA. Also, although RhoA/Rho kinase played a significant role in PDBu-mediated contractions of FN CA, this was not the case in FH or either adult group. Also, whereas CPI-17 had a significant role in adult CA contractility, this was not the case for the fetus. Overall, in ovine CA, the present study demonstrates several important maturational and LTH acclimatization changes in PKC-induced contractile responses and downstream pathways. The latter may play a key role in the pathophysiologic disorders associated with acclimatization to high altitude. Keywords:high altitude, fetus, ERK1/2, RhoA, 20-kDa myosin light chain, CPI-17 for the developing fetusin utero, hypoxia constitutes a stress of critical importance. Severe acute hypoxia or more moderate prolonged hypoxia can result in major neurological sequelae with life-long consequences. In normoxic near-term sheep, in response to acute hypoxia [arterial FD 12-9 Po2(PaO2) = 12 1 Torr], we previously demonstrated a decrease in fetal cortical tissue Po2from 9 1 to 2 2 1 Torr and a 48 10% increase in relative cerebral blood flow (CBF) (33). In contrast, in a related study in the fetus acclimatized to high-altitude long-term hypoxia (LTH), superimposed acute hypoxia had FD 12-9 significantly less effect on increasing CBF (19 2%) or decreasing cerebral oxygenation (cortical tissue Po2decreased from 6 1 to 2 2 1 Torr) than in sea-level controls (3,48,58,59). In adults who ascend to high altitude with associated hypoxia, initially CBF increases by vasodilation and then, as the process of acclimatization occurs, returns to near-normal values (26,55). This CBF acclimatization response is regulated by a number of factors that alter the activity of arterial smooth muscle cell surface receptors and signal transduction cascade to modulate cerebrovascular tone via inositol trisphosphate-dependent Ca2+release from intracellular stores and to augment intracellular Ca2+concentration ([Ca2+]i) (18) and a PKC Ca2+-independent/sensitization pathway (19). Ca2+-dependent and -independent pathways produce a contractile response by regulating thin-filament (actin) and thick-filament (myosin) interaction. The most-studied myosin is a 20-kDa regulatory myosin light chain (MLC20) filament pathway, the activity of which depends on the balance of activities of MLC kinase (MLCK, which phosphorylates MLC20) and MLC phosphatase (MLCP, which dephosphorylates MLC20) (23,56). MLCP and MLCK activities are regulated by a complex signal transduction cascade/network that includes modulation by PKC, as well as by other kinases and pathways. Critical components of the PKC-mediated pathway Mouse monoclonal to PTK7 include MAPK (2), ERK1 and ERK2 (ERK1/2) (2,4), and Rho kinase (ROCK), the 17-kDa PKC-potentiated myosin phosphatase inhibitor CPI-17, and other enzymes (19,25). Although the relation of PKC-ERK activation to gene expression with cell proliferation and differentiation is well established (8), less is known of the roles of this signaling pathway in vascular smooth muscle contractility. During the past decade, accumulating evidence from our and other laboratories has suggested that components of the MAPK cascade may be involved in vascular contraction, via altered sensitivity of the contractile machinery (10,14,22,30,69,74). Recently, we demonstrated that, with maturation from fetus to adult, there is a significant alteration in these cerebral artery (CA) PKC-activated downstream signaling pathways (19). However, the extent to which these developmentally associated changes result from maturation, per se, or from oxygenation, FD 12-9 as the fetus (PaO225 2 Torr) is in a relative hypoxemic state compared with the adult (PaO295 5 Torr) (28,33), is unknown. With PKC, along with ERK1/2 and RhoA, activation, myofilament Ca2+sensitization occurs through its effector ROCK, which, in turn, modulates vascular smooth muscle sensitivity to [Ca2+]iby inhibiting the MLCP activity, thus enhancing MLC20phosphorylation (9,35,56,57,64). Recently, we.