Calmodulin (CaM) is a calcium-binding protein that has promiscuous regulatory interactions with over three hundred intracellular protein targets. The focus of this study was to characterize the functional role of phosphorylated CaM in vitro and calcium-deficient CaM (Apo-CaM) ex vivo. In the in vitro study, the effect of phosphorylated CaM on the binding and activation of CaM target proteins was analyzed using mammalian Nitric Oxide Synthase (NOS). NOS is an enzyme that catalyzes the conversion of L-arginine to L-citrulline and •NO. In addition, the activation of NOS by modified CaM proteins was also analyzed in the presence of a CaM binding peptide, PEP-19. Protein trafficking experiments were performed ex vivo to extend our understanding of Apo-CaM’s functional role in mammalian cells. The cell lines that were used in this investigation include mouse Embryonic Stem Cells (mESC), Human Umbilical Vein Endothelia Cells (HUVEC) and Human Neuronal Glioma Cells (HNGC). The major finding of this projects are: phosphorylation of selective CaM residues can attenuated NOS activity, electrostatic interactions are important in the activation of iNOS by CaM, and the activation of iNOS by CaM occurs in a calcium-dependent manner

Thesis (M. Med. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 53-67).

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Not available / text

No description available.

Orthostatic intolerance following exposure to simulated or actual microgravity is observed following spaceflight and extended periods of bed rest, and is not always associated with simultaneous hypotension. Differential adaptation of cephalic and caudal arterial vasculatures (as a result of removal of the normal hydrostatic gradient) is proposed as a potential mechanism underlying this phenomenon. A potential role for changes to the L-arginine/nitric oxide pathway in such adaptations has been suggested, predominantly from previous in vitro studies; using an established model of simulated microgravity (head-down tilt; HDT). This thesis investigates whether findings in isolated vessels are reflected by in vivo measurements of cephalic and caudal vascular function. Using carotid or iliac artery flow normalized to mean arterial pressure as an index of cerebral or hind limb vascular conductance, autoregulatory cerebral vasodilatation in response to lower body negative pressure was found to be impaired following HDT. In addition, α¬1-adrenoceptor agonist-mediated vasoconstriction was decreased in the cerebral vasculature and increased in the peripheral and hind limb vasculature. Administration of acetylcholine or the non-selective nitric oxide synthase (NOS) inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) demonstrated a decreased contribution of NOS to cerebrovascular tone, but an increased contribution of NOS to peripheral vascular resistance and tone of the hind limb vasculature. Together with a lack of difference in the response to the selective inducible NOS (iNOS) inhibitor 1400W, these results suggest that differential adaptation of eNOS may account for the observed differences between control and HDT animals. Further investigation of the changes to the L-arginine/nitric oxide pathway suggest that these changes are not associated with changes in eNOS expression, but may be related to altered activity of eNOS. Furthermore, the bioavailability (as measured by pharmacokinetic half life) or the vascular effector mechanisms (as measured by the haemodynamic response to exogenously administered nitric oxide) responsible for the effects of nitric oxide were also shown to be unaffected by HDT. These findings suggest that differential adaptation of the L-arginine/nitric oxide pathway may contribute to the inability to raise total peripheral resistance and impaired cerebral autoregulation following HDT, thereby representing a mechanism of orthostatic intolerance following exposure to microgravity.

No description available.

Orthostatic intolerance following exposure to simulated or actual microgravity is observed following spaceflight and extended periods of bed rest, and is not always associated with simultaneous hypotension. Differential adaptation of cephalic and caudal arterial vasculatures (as a result of removal of the normal hydrostatic gradient) is proposed as a potential mechanism underlying this phenomenon. A potential role for changes to the L-arginine/nitric oxide pathway in such adaptations has been suggested, predominantly from previous in vitro studies; using an established model of simulated microgravity (head-down tilt; HDT). This thesis investigates whether findings in isolated vessels are reflected by in vivo measurements of cephalic and caudal vascular function. Using carotid or iliac artery flow normalized to mean arterial pressure as an index of cerebral or hind limb vascular conductance, autoregulatory cerebral vasodilatation in response to lower body negative pressure was found to be impaired following HDT. In addition, α¬1-adrenoceptor agonist-mediated vasoconstriction was decreased in the cerebral vasculature and increased in the peripheral and hind limb vasculature. Administration of acetylcholine or the non-selective nitric oxide synthase (NOS) inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) demonstrated a decreased contribution of NOS to cerebrovascular tone, but an increased contribution of NOS to peripheral vascular resistance and tone of the hind limb vasculature. Together with a lack of difference in the response to the selective inducible NOS (iNOS) inhibitor 1400W, these results suggest that differential adaptation of eNOS may account for the observed differences between control and HDT animals. Further investigation of the changes to the L-arginine/nitric oxide pathway suggest that these changes are not associated with changes in eNOS expression, but may be related to altered activity of eNOS. Furthermore, the bioavailability (as measured by pharmacokinetic half life) or the vascular effector mechanisms (as measured by the haemodynamic response to exogenously administered nitric oxide) responsible for the effects of nitric oxide were also shown to be unaffected by HDT. These findings suggest that differential adaptation of the L-arginine/nitric oxide pathway may contribute to the inability to raise total peripheral resistance and impaired cerebral autoregulation following HDT, thereby representing a mechanism of orthostatic intolerance following exposure to microgravity.

Thesis (Ph. D.)--Georgia State University, 2007. / Vincent Rehder, committee chair; Sarah Pallas, Walter William Walthall, committee members. Electronic text (248 p. : ill. (some col.)) : digital, PDF file. Description based on contents viewed Jan. 28, 2008; title from file title page. Includes bibliographical references (p. 218-248).