Effects of metabolic inhibition on cytoplasmic calcium and contraction in smooth muscle of rat portal vein
Author
Summary, in English
Contractions in the rat portal vein, evoked by spontaneous action potentials or depolarizing high-K+ solution, are rapidly and reversibly inhibited by hypoxia or respiratory blockade. Intracellular free calcium ([Ca2+]i) was measured using Fura-2 to evaluate the effects of metabolic blockade on excitation-contraction coupling. Spontaneous contractions were associated with transient increases in [Ca2+]i. During exposure to cyanide (0.2-0.4 mM) or 2,4-dinitrophenol (30 microM) the duration and amplitude of the Ca2+ transients were decreased, leading to a decreased mean time integral of the individual [Ca2+]i transient, and corresponding decrease in the duration and amplitude of the contraction. Basal [Ca2+]i was increased in the presence of the metabolic inhibitors. High-K+ (40 mM) contractions caused a sustained increase in [Ca2+]i, which was not inhibited by exposure to cyanide, although the amplitude of the associated contraction was greatly reduced. Together with the earlier demonstration of decreased 20 kD myosin light chain phosphorylation under these conditions, this indicates that the activation of contraction is influenced by metabolism via the energy dependence of the light chain phosphorylation reaction. Thus at least three steps in the excitation-contraction sequence are influenced by inhibition of oxidative metabolism: membrane excitation, light chain phosphorylation, and the cross-bridge cycle. This provides mechanisms for a high degree of metabolic sensitivity of vascular tone, of importance for the adaptation of blood flow to tissue metabolic demands.
Publishing year
1993
Language
English
Pages
265-272
Publication/Series
Acta Physiologica Scandinavica
Volume
148
Issue
3
Document type
Journal article
Publisher
Wiley-Blackwell
Topic
- Physiology
Status
Published
Research group
- Vascular Physiology
ISBN/ISSN/Other
- ISSN: 0001-6772