Cellular Mechanisms Underlying Myogenic Reactivity in Isolated Arterioles
The myogenic reactivity provides one of the principal mechanisms for blood flow autoregulation. The aims of the performed studies described in this dissertation were to test the role of [Ca2+]i and MLC phosphorylation in arteriolar myogenic reactivity and further examine the source(s) of activator Ca2+ required to initiate and maintain myogenic vasoconstriction. In addition, the possible underlying mechanism of contractile protein expression was also addressed. These studies used male Sprague Dawley rats of 200 ~ 350 grams body weight. Experiments were carried out using rat cremaster first order arterioles and mesenteric vessels. Gel electrophoresis and immunoblotting techniques were employed to analyze and identify the contractile protein isoforms and myosin light chain phosphorylation while the functional aspects of the studies were performed on isolated cannulated vessel preparations. Intracellular calcium was measured using a video based image system with fura-2 as a fluorescent Ca2+ indicator. A fluorescence image intensity ratio of 340nm over 380nm excitation wavelengths was accepted as a measurement of [Ca2+]i. Samples for measuring MLC phosphorylation were collected by quickly freezing the vessels at the desired time points after different treatments according to the computerized image analysis system. The following conclusions were drawn from the studies presented in this dissertation: 1) Myogenic reactivity may, in part, relate to differences in structural composition of contractile proteins; 2) [Ca2+]i and MLC phosphorylation play obligatory roles in the setting of arteriolar spontaneous tone and myogenic reactivity; 3) Wall tension appears to be the detected variable and a regulatory factor during the arteriolar myogenic reactivity; 4) α-adrenergic agonist induced-arteriolar contraction also depends on increases in [Ca2+]i and MLC phosphorylation, however, signaling pathways appear to differ from that described for myogenic contraction. Further, mechanisms involving the contractile element Ca2+ sensitization also contribute to the agonist-induced response; 5) The extracellular Ca2+ source is most important in the maintenance of arteriolar basal tone and the myogenic contraction. While Ca2+ entry from the extracellular environment, largely via VOCs, is a mandatory process, Ca2+ release from intracellular stores may also be involved in the myogenic constriction. An additional Ca2+ entry mechanism, possibly receptor-operated Ca2+ channels, is involved in the agonist-induced contractions.
Blood flow, Calcium, Phosphorylation, Anatomy, Animal Structures, Cell Biology, Physiology
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