Long-term effects of intracellular calcium and growth factors on excitation and contraction in smooth muscle.
Modulation of vascular smooth muscle cells from a contractile to a synthetic phenotype is thought to be important in the development of the atherosclerotic lesion. Such modulation depends on growth factors and is influenced by cell-cell and cell-matrix interactions. Whereas smooth muscle cells in the vessel wall are contractile, dispersed cells in culture rapidly modulate to synthetic phenotype, which complicates long-term in vitro studies. In contrast, vascular segments or smooth muscle strips in organ culture can maintain contractility for at least a week, sufficient for studies involving altered metabolism or protein expression. Examples are effects of endogenous polyamines on membrane ion channels and excitation-contraction coupling. While smooth muscle tissue is well preserved in serum-free culture, growth stimulation with fetal calf serum (FCS) causes multiple effects, including decreased contractility, ultrastructural changes, decreased expression of L-type Ca2+ channels, and increased SR release of Ca2+ via ryanodine receptors. These are all consequences of increased basal [Ca2+]i caused by FCS, as they are reversed by culture with verapamil in a concentration (1 microM) that does not inhibit stimulation of DNA and protein synthesis by FCS. The effects of FCS on contractility and Ca2+ channel expression are mimicked in serum-free culture with increased [Ca2+]i. Contractile protein patterns, including myosin isoform composition, are unaffected by FCS, suggesting that reversal to synthetic phenotype is limited and not the immediate cause of decreased contractility.
Hellstrand
P
P
Department of Physiology and Neuroscience, Lund University, Sweden.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D003285:Contractile Proteins / Q000737:chemistry / Q000502:physiology; D006133:Growth Substances / Q000502:physiology*; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*
D003285:Contractile Proteins; D006133:Growth Substances; D002118:Calcium