Ca²⁺‐pumps and Na⁺–Ca²⁺‐exchangers in coronary artery endothelium versus smooth muscle

Abstract

Vascular endothelial cells (EC) and smooth muscle cells (SMC) require a decrease in cytoplasmic Ca2+ concentration after activation. This can be achieved by Ca2+ sequestration by the sarco-/endoplasmic reticulum Ca2+ pumps (SERCA) and Ca2+ extrusion by plasma membrane Ca2+ pumps (PMCA) and Na+–Ca2+-exchangers (NCX). Since the two cell types differ in their structure and function, we compared the activities of PMCA, NCX and SERCA in pig coronary artery EC and SMC, the types of isoforms expressed using RT-PCR, and their protein abundance using Western blots. The activity of NCX is higher in EC than in SMC but those of PMCA and SERCA is lower. Consistently, the protein abundance for NCX protein is higher in EC than in SMC and those of PMCA and SERCA is lower. Based on RT-PCR experiments, the types of RNA present are as follows: EC for PMCA1 while SMC for PMCA4 and PMCA1; EC for SERCA2 and SERCA3 and SMC for SERCA2. Both EC and SMC express NCX1 (mainly NCX1.3). PMCA, SERCA and NCX differ in their affinities for Ca2+ and regulation. Based on these observations and the literature, we conclude that the tightly regulated Ca2+ removal systems in SMC are consistent with the cyclical control of contractility of the filaments and those in EC are consistent with Ca2+ regulation of the endothelial nitric oxide synthase near the cell surface. The differences between EC and SMC should be considered in therapeutic interventions of cardiovascular diseases.

Update on vascular endothelial Ca2+signalling: A tale of ion channels, pumps and transporters

“…The electrochemical gradient for Na + provides the energy necessary to drive Ca 2+ out of the cell against its large gradient and with a stoichiometric ratio of 3 Na + in: 1 Ca 2+ out [366] . Cultured ECs may express all of the three NCX subtypes [355,367,368] , while the only evidence about NCX presence in situ has been reported in rat brain [369] . NCX expression may be upregulated by an increase in [Ca 2+ ]i [370] .…”

“…The SERCA isoforms differ mainly by their affinity for Ca 2+ (2b > 2a = 1 >> 3) and their Ca 2+ transport turnover rates, SERCA2b having the lowest transport capacity of all SERCAs [350] . Both SERCA2a and SERCA3 have been found in isolated and in situ ECs [106,[351][352][353][354][355][356] , albeit SERCA3 transcript levels decrease during EC proliferation in culture and in hypertension [106,112] . SERCA3 expression is regulated by Ca 2+ itself in a calcineurin/NFAT-dependent manner [357] and its genetic deletion leads to a decrease in agonist-induced elevation in [Ca 2+ ]i and NO synthesis [358] .…”

Plasma membrane calcium ATPases (PMCAs) as potential targets for the treatment of essential hypertension

“…In contrast, others have shown that mRNA for PMCA1 is more prevalent than that for PMCA4 in rat cultured aortic VSMCs, with PMCA4 transcripts suggested to be at only a quarter of the level of those for PMCA1 (Sasamura et al, 2002). In porcine aortic endothelial cells PMCA1 RNA has been shown to be detectable at a higher level than PMCA4 transcripts (Pande et al, 2006;Szewczyk et al, 2007). Thus, the vascular expression of PMCA1 and 4 may be species specific, with further work being required to clearly determine the relative expression of PMCA1 and PMCA4 in VSMCs and endothelial cells, particularly in resistance arteries.…”

“…PMCA4 mRNA has been detected in endothelial and VSMCs of porcine aorta (Szewczyk et al, 2007), in VSMCs from mouse carotid artery , and was shown as the most prominent PMCA mRNA transcript in mouse whole aorta (Okunade et al, 2004). PMCA4 protein expression has been reported in a mouse VSMC line and in isolated murine aortic VSMCs .…”

“…PMCA1 RNA has been detected in pig aortic smooth muscle and endothelial cells (Pande et al, 2006), whilst mRNA for PMCA1 has also been detected in rat cultured aortic VSMCs (Sasamura et al, 2002). At the protein level, PMCA1 is present in VSMCs from mouse aorta (Kobayashi et al, 2012), as well as in endothelial cells from the pig coronary artery (Szewczyk et al, 2007).…”