Rat aortic smooth muscle cells contract in response to serum and its components in a calcium independent manner

Diluted serum provides a model of interstitial fluid that can be used to study the response of smooth Muscle cells (SMCs) to interstitial flow. The effect of serum and some of its components on SMC contraction (area reduction) and intracellular calcium ([Ca2+](i)) response were characterized in rat aortic SMC in vitro. Rat aortic SMCs contracted dramatically to fetal bovine serum (FBS), bovine serum albumin (BSA), and lysophosphatidic acid (LPA) within 5 min of exposure. By 30 min, cell areas were significantly reduced. Even at concentrations as low as 0.0005% FBS, 0.004% BSA and 0.25 muM LPA, cell areas were significantly different from controls at 30 min. The [Ca2+](i) response was significant for serum and LPA at these low concentration levels, but BSA did not elicit a significant [Ca2+](i) response at concentrations of 0.1% or lower. Under calcium controlled conditions in which SMCs were pretreated with 10 muM BAPTA-AM, contraction levels were not statistically different from non-calcium controlled conditions even when SMCs were exposed to the highest concentration of serum, BSA, or LPA. It appears that LPA and albumin are components of interstitial fluid that contribute to SMC contraction through calcium-independent mechanisms.