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

Culture of dispersed smooth muscle cells is known to cause rapid modulation from the contractile to the synthetic cellular phenotype. However, organ c ulture of smooth muscle tissue, with maintained extracellular matrix and ce ll-cell contacts, may facilitate maintenance of the contractile phenotype. To test the influence of culture conditions, structural, functional, and bi ochemical properties of rat tail arterial rings were investigated after cul ture. Rings were cultured for 4 days in the absence and presence of 10% FCS and then mounted for physiological experiments. Intracellular Ca2+ concent ration ([Ca2+](i)) after stimulation with norepinephrine was similar in rin gs cultured with and without FCS, whereas force development after FCS was d ecreased by >50%. The difference persisted after permeabilization with beta -escin. These effects were associated with the presence of vasoconstrictors in FCS and were dissociated from its growth-stimulatory action. FCS treatm ent increased lactate production but did not affect ATP, ADP, or AMP conten ts. 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/SMB isoform composition, nor was there any appearance of non muscle myosin. FCS-stimulated rings showed evidence of cell degeneration no t found after culture without FCS or with FCS + verapamil (1 mu M) to lower [Ca2+](i). The decreased force-generating ability after culture with FCS i s thus associated with increased [Ca2+](i) during culture and not primarily caused by growth-associated modulation of cells from the contractile to th e synthetic phenotype.