Increased store-operated Ca2+ entry into contractile vascular smooth muscle following organ culture
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Ca2+ inflow via store-operated Ca2+ channels was investigated in rings of rat tail and basilar arteries kept in serum-free organ culture, which is known to preserve the contractility of the vascular smooth muscle. After culture for 3-4 days, Ca2+ release from intracellular stores in response to caffeine (20 mM) was augmented 2- to 4-fold. Following depletion of intracellular Ca2+ stores by caffeine and thapsigargin (10 microM), addition of Ca2+ (2.5 mM) caused an increase in the intracellular Ca2+ concentration which was 2-3 times greater in cultured than in freshly dissected rings, and was not affected by verapamil (10 microM). In contrast, L-type Ca2+ channel currents were decreased by 20% after culture. While freshly dissected rings developed no or very little force in response to the addition of Ca2+ after store depletion, cultured rings developed 42% (tail artery) and 60% (basilar artery) of the force of high-K+-induced contractions. These contractions in cultured vessels were insensitive to verapamil but could be completely relaxed by SKF-96365 (30 microM). Store depletion by caffeine increased the Mn2+ quench rate 3- to 4-fold in freshly dissected as well as cultured tail artery, while there was no increase in freshly dissected basilar artery, but a 3-fold increase in cultured basilar artery. Uptake of Ca2+ into intracellular stores was twice as rapid in cultured as in freshly dissected tail artery. This study shows that organ culture of vascular smooth muscle tissue causes changes in Ca2+ handling, resembling the pattern seen in dedifferentiating smooth muscle cells in culture, although contractile properties are maintained.