Maturation of intracellular calcium homeostasis in sheep pulmonary arterial smooth muscle cells

Goyal R, Creel KD, Chavis E, Smith GD, Longo LD, Wilson SM. Maturation of intracellular calcium homeostasis in sheep pulmonary arterial smooth muscle cells. Am J Physiol Lung Cell Mol Physiol 295: L905-L914, 2008. First published September 5, 2008; doi:10.1152/ajplung.00053.2008. - Cytosolic Ca2+ signaling dynamics are important to pulmonary arterial reactivity, and alterations are implicated in pulmonary vascular disorders. Yet, adaptations in cellular Ca2+ homeostasis and receptor-mediated Ca2+ signaling with maturation from fetal to adult life in pulmonary arterial smooth muscle cells (PASMCs) are not known. The present study tested the hypothesis that cytosolic Ca2+ homeostasis and receptor-generated Ca2+ signaling adapt with maturation in sheep PASMCs. Digitalized fluorescence microscopy was performed using isolated PASMCs from fetal and adult sheep that were loaded with the Ca2+ indicator fura 2. The results show that basal cytosolic and sarcoplasmic reticulum Ca2+ levels are attained before birth. Similarly, Ca2+ efflux pathways from the cytosol and basal as well as capacitative Ca2+ entry (CCE) are also developed before birth. However, receptor-mediated Ca2+ signaling adapts with maturation. Prominently, serotonin stimulation elicited Ca2+ elevations in very few fetal compared with adult PASMCs; in contrast, phenylephrine elevated Ca2+ in a similar percentage of fetal and adult PASMCs. Serotonin and phenylephrine elicited Ca2+ increases of a similar magnitude in reactive cells of fetus and adult, supporting the assertion that inositol trisphosphate signaling is intact. Caffeine and ATP elevated Ca2+ in equivalent numbers of fetal and adult PASMCs. However, the caffeine-induced cytosolic Ca2+ increase was significantly greater in fetal PASMCs, whereas the ATP-elicited increase was greater in adult cells. Overall, the results of this study demonstrate selective adaptations in receptor-mediated Ca2+ signaling, but not in cellular Ca2+ homeostasis.