Submitted on January 31, 2008
Accepted on August 25, 2008
Maturation of intracellular calcium homeostasis in sheep pulmonary arterial smooth muscle cells
Ravi Goyal1, Kara D Creel1, Erica J Chavis1, Gregory D. Smith2, Lawrence D Longo3, and Sean M Wilson4*
1 Pharmacology, University of Mississippi School of Pharmacy, University, Mississippi, United States
2 Department of Applied Science, College of William and Mary, Williamsburg, Virginia, United States
3 Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda , California, United States
4 Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, California, United States
* To whom correspondence should be addressed. E-mail: seanwilson{at}llu.edu.
Cytosolic calcium (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 (5-HT) stimulation elicited Ca2+ elevations in very few fetal PASMCs as compared to adult; in contrast, phenylephrine (PE) was able to produce Ca2+ elevations in similar percentage of fetal and adult PASMCs. Of interest, 5-HT and PE elicited Ca2+ increases of a similar magnitude in reactive cells of fetus and adult, supporting the assertion that IP3 signaling is intact. Caffeine and ATP produced Ca2+ elevations in equivalent numbers of fetal and adult PASMCs. However, the cytosolic Ca2+ increase to caffeine was significantly greater in fetal PASMCs, while ATP produced greater Ca2+ elevations in adult. Overall, the results of this study demonstrate selective adaptations in receptor mediated Ca2+ signaling, but not in the cellular Ca2+ homeostasis.
