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- Ekmehag, Björn, et al.
(author)
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Contractile and metabolic characteristics of creatine-depleted vascular smooth muscle of the rat portal vein
- 1988
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In: Acta Physiologica Scandinavica. - 0001-6772. ; 133:4, s. 525-533
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Journal article (peer-reviewed)abstract
- The functional consequences of phosphocreatine (PCr) depletion for mechanical properties, O2 consumption, and lactate production of the rat portal vein were investigated. After feeding rats for 8-9 weeks on a diet containing 2% beta-guanidino propionic acid (BGPA), PCr of the portal vein was reduced to 14% of control, whereas ATP was unchanged. No significant change was found in the level of spontaneous contractile activity or the force developed in a high-K+ contracture. Lactate production and the relationship between contractile force and O2 consumption were uninfluenced by BGPA treatment. The force-velocity relation of electrically stimulated portal veins showed no influence of BGPA treatment on Vmax. To investigate whether decrease in PCr influenced the response to metabolic stress, portal veins were exposed to graded concentrations (0.1-0.5 mM) of cyanide to depress cellular respiration. Veins from control and BGPA-treated rats showed the same relative decrease of contractile activity and O2 consumption, and the same increase in lactate production. Cyanide treatment resulting in a reduction of electrically stimulated force to 70-80% of the original gave a reduction of Vmax to 85-90%. The relative degree of reduction was uninfluenced by BGPA treatment. Reduction of PCr content thus does not affect the functional properties of metabolism or contractility under normoxic conditions. Furthermore, it can be inferred that the PCr reduction known to occur in smooth muscle exposed to hypoxia (Lovgren & Hellstrand 1985) is not in itself the major factor causing hypoxic inhibition of mechanical activity.
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| 2. |
- Ekmehag, Björn, et al.
(author)
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Shortening velocity, myosin light chain phosphorylation and Ca2+ dependence of force during metabolic inhibition in smooth muscle of rat portal vein
- 1989
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In: Acta Physiologica Scandinavica. - 0001-6772. ; 136:3, s. 367-376
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Journal article (peer-reviewed)abstract
- The concentration-response relation for Ca2+ (0.2-5.0 mM) of high-K+ contractures (40 mM) in the rat portal vein during respiratory inhibition by 0.2 mM cyanide was investigated. A reduction of force in the presence of cyanide to about 30% of control was associated with a leftward shift of the normalized concentration-response relation. When force at the plateau of high-K+ contractures (at about 2 min) was reduced to 65 +/- 2% due to the addition of cyanide, the maximal shortening velocity (Vmax) was 94 +/- 5% of control (n = 6). In electrically (AC) stimulated preparations giving short tetanic contractions, a reduction of active force to 58 +/- 2% of control in the presence of cyanide was associated with a reduction of Vmax to 83 +/- 5% (n = 7). Phosphorylation of the 20-kDa regulatory light chains (LC20) of the myosin molecule was studied in the relaxed state and at the plateau of high-K+ contractures for comparison with the mechanical data. Both control and cyanide-treated preparations showed 9% LC20 phosphorylation in nominally Ca2+-free solution (n = 6). After activation the level of phosphorylation increased to 30 +/- 3% (n = 9) in the control veins. In cyanide-treated veins, where force was reduced to 42 +/- 6% compared to a preceding control period, the phosphorylation level was 17 +/- 2% (n = 7). The study suggests that the mechanical changes caused by inhibition of cellular respiration may involve the combined effect of several metabolic alterations, including decreased LC20 phosphorylation during contraction, but apparently not decreased intracellular Ca2+ concentration or sensitivity of the contractile system to Ca2+.
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