Long-term effects of Ca²⁺ on structure and contractility of vascular smooth muscle

Abstract

Culture of dispersed smooth muscle cells is known to cause rapid modulation from the contractile to the synthetic cellular phenotype. However, organ culture of smooth muscle tissue, with maintained extracellular matrix and cell-cell contacts, may facilitate maintenance of the contractile phenotype. To test the influence of culture conditions, structural, functional, and biochemical properties of rat tail arterial rings were investigated after culture. Rings were cultured for 4 days in the absence and presence of 10% FCS and then mounted for physiological experiments. Intracellular Ca2+concentration ([Ca2+]i) after stimulation with norepinephrine was similar in rings cultured with and without FCS, whereas force development after FCS was decreased by >50%. The difference persisted after permeabilization with β-escin. These effects were associated with the presence of vasoconstrictors in FCS and were dissociated from its growth-stimulatory action. FCS treatment increased lactate production but did not affect ATP, ADP, or AMP contents. The contents of actin and myosin were decreased by culture but similar for all culture conditions. There was no effect of FCS on calponin contents or myosin SM1/SM2 isoform composition, nor was there any appearance of nonmuscle myosin. FCS-stimulated rings showed evidence of cell degeneration not found after culture without FCS or with FCS + verapamil (1 μM) to lower [Ca2+]i. The decreased force-generating ability after culture with FCS is thus associated with increased [Ca2+]iduring culture and not primarily caused by growth-associated modulation of cells from the contractile to the synthetic phenotype.

Influence of Mitochondrial Inhibition on Global and Local [Ca 2+ ] i in Rat Tail Artery

“…A central consideration in interpreting the present results is whether an altered wave pattern toward increased frequency and decreased amplitude is able to explain a decrease in force production in spite of maintained (or at least nearly so) levels of global [Ca 2ϩ ] adrenergic stimulation in the tail artery, 18 force was considerably reduced for similar Ca 2ϩ levels during mitochondrial inhibition. A further prediction of the model is that force can be reduced as a consequence of reduced interwave [Ca 2ϩ ] i because this would affect the position of the wave peaks vis à vis the threshold for contraction.…”

“…Rings (1 mm wide) were mounted for isometric force registration as described. 18 After equilibration in Krebs solution containing 2.5 mmol/L Ca 2ϩ for 30 minutes at 37°C, preparations were repeatedly contracted with 0.3 mol/L cirazoline (7 minutes) followed by relaxation for 25 minutes, until stable contractions were attained and experimentation begun. ] i oscillations by the total number of cells in the field (maximally 60 cells).…”

Plasticity of TRPC expression in arterial smooth muscle: correlation with store-operated Ca2+ entry

“…Serum-free organ culture of intact vessels preserves contractility and does not stimulate cell proliferation (17) but is associated with altered Ca 2ϩ handling (4,5), suggesting that a slow shift in phenotype occurs. Dissection of a blood vessel and placement in an artificial medium necessarily constitutes trauma, which is expected to cause a tissue reaction.…”

“…Organ culture of intact vascular tissue has been shown to preserve contractile differentiation for several days, although subtle changes in cellular properties occur (11). Progression of cellular alterations is considerably slowed when vessels are cultured in the absence of added growth factors such as fetal calf serum (17), although endothelial integrity is disturbed and changes in membrane properties occur as observed with respect to receptor expression for PDGF and endothelin (ET) (20). Prolonged culture of human and porcine vessels has been shown to cause the formation of a neointima, which is a lesion characteristic of restenosis after angioplasty (15,25).…”

Rat arterial smooth muscle devoid of ryanodine receptor function: effects on cellular Ca2+ handling

“…This is close to the optimal preload for these preparations (Lindqvist et al, 1999). Preparations were immersed in warm HEPES-buered solution containing (mM): NaCl 135.5, KCl 5.9, CaCl 2 2.5, MgCl 2 1.2, N-2-hydroxyethyl-piperazine-N'-2-ethanesulphonic acid (HEPES) 11.6, and glucose 11.5.…”