Heterogeneity of calcium stores and elementary release events in canine pulmonary arterial smooth muscle cells

Abstract

To examine the nature of inositol 1,4,5-trisphosphate (IP(3))-sensitive and ryanodine (Ryn)-sensitive Ca(2+) stores in isolated canine pulmonary arterial smooth cells (PASMC), agonist-induced changes in global intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured using fura 2-AM fluorescence. Properties of elementary local Ca(2+) release events were characterized using fluo 3-AM or fluo 4-AM, in combination with confocal laser scanning microscopy. In PASMC, depletion of sarcoplasmic reticulum Ca(2+) stores with Ryn (300 microM) and caffeine (Caf; 10 mM) eliminated subsequent Caf-induced intracellular Ca(2+) transients but had little or no effect on the initial IP(3)-mediated intracellular Ca(2+) transient induced by ANG II (1 microM). Cyclopiazonic acid (CPA; 10 microM) abolished IP(3)-induced intracellular Ca(2+) transients but failed to attenuate the initial Caf-induced intracellular Ca(2+) transient. These results suggest that in canine PASMC, IP(3)-, and Ryn-sensitive Ca(2+) stores are organized into spatially distinct compartments while similar experiments in canine renal arterial smooth muscle cells (RASMC) reveal that these Ca(2+) stores are spatially conjoined. In PASMC, spontaneous local intracellular Ca(2+) transients sensitive to modulation by Caf and Ryn were detected, exhibiting spatial-temporal characteristics similar to those previously described for "Ca(2+) sparks" in cardiac and other types of smooth muscle cells. After depletion of Ryn-sensitive Ca(2+) stores, ANG II (8 nM) induced slow, sustained [Ca(2+)](i) increases originating at sites near the cell surface, which were abolished by depleting IP(3) stores. Discrete quantal-like events expected due to the coordinated opening of IP(3) receptor clusters ("Ca(2+) puffs") were not observed. These data provide new information regarding the functional properties and organization of intracellular Ca(2+) stores and elementary Ca(2+) release events in isolated PASMC.

Ca2+ entry following P2X receptor activation induces IP3 receptor‐mediated Ca2+ release in myocytes from small renal arteries

“…The initial Ca 2+ mobilization may be augmented by RyR-mediated Ca 2+ release recruited via a CICR mechanism (Bolton and Gordienko, 1998;Bayguinov et al, 2000;White and McGeown, 2002;Kotlikoff, 2003;Zhang et al, 2003;Hotta et al, 2007;Gordienko et al, 2008). The contribution of these mechanisms to intracellular Ca 2+ mobilization may vary in different SMC types, depending on the type and strength of stimuli, SMC excitability and spatial organisation of intracellular Ca 2+ release units (Walsh, 1994;Bolton and Gordienko, 1998;Bolton et al, 1999;Davis and Hill, 1999;Bayguinov et al, 2000;Gordienko et al, 2001Gordienko et al, , 2008Janiak et al, 2001;Gordienko and Bolton, 2002;White and McGeown, 2002;Kotlikoff, 2003;Wier and Morgan, 2003;Zhang et al, 2003;Lamont and Wier, 2004;McCarron et al, 2006;Amberg et al, 2007;Hotta et al, 2007;Wier et al, 2009).…”

“…The initial Ca 2+ mobilization may be augmented by RyR-mediated Ca 2+ release recruited via a CICR mechanism (Bolton and Gordienko, 1998;Bayguinov et al, 2000;White and McGeown, 2002;Kotlikoff, 2003;Zhang et al, 2003;Hotta et al, 2007;Gordienko et al, 2008). The contribution of these mechanisms to intracellular Ca 2+ mobilization may vary in different SMC types, depending on the type and strength of stimuli, SMC excitability and spatial organisation of intracellular Ca 2+ release units (Walsh, 1994;Bolton and Gordienko, 1998;Bolton et al, 1999;Davis and Hill, 1999;Bayguinov et al, 2000;Gordienko et al, 2001Gordienko et al, , 2008Janiak et al, 2001;Gordienko and Bolton, 2002;White and McGeown, 2002;Kotlikoff, 2003;Wier and Morgan, 2003;Zhang et al, 2003;Lamont and Wier, 2004;McCarron et al, 2006;Amberg et al, 2007;Hotta et al, 2007;Wier et al, 2009).We hypothesized that in vascular myocytes Ca 2+ entry following activation of ionotropic P2X receptors may induce IP3R-mediated Ca 2+ release. Our hypothesis was based on the following findings reported in visceral and vascular myocytes: (i) a localized increase in [Ca 2+ ]i induced by local flash release of Ca 2+ from a 'caged' precursor may trigger IP3R-mediated Ca 2+ release (Ji et al, 2006); (ii) Ca 2+ entry via VGCCs facilitates IP3R-mediated Ca 2+ release following stimulation of metabotropic receptors (Gordienko et al, 2008); (iii) the stoichiometric ratio of RyRs to IP3Rs in SMCs is 1:9-10, suggesting the existence of a Ca 2+ -storage compartment devoid of RyRs but equipped with IP3Rs (Wibo and Godfraind, 1994); (iv) caffeine/ryanodinereleasable and IP3-releasable calcium stores in the SR of vascular myocytes are at least partially distinct with about 56% of the SR being solely IP3-sensitive (Blauste...…”

Spatial and temporal traction response in human airway smooth muscle cells

“…10). Calcium concentration is spatially inhomogeneous throughout the cytoplasm: local Ca 2ϩ transients, named Ca 2ϩ sparks, occur spontaneously in smooth muscle cells (14,15,25). Pabelick et al (24) showed that spark amplitude and occurrence varies considerably across different regions of the cells.…”

Calcium Mobilization via Intracellular Ion Channels, Store Organization and Mitochondria in Smooth Muscle

“…With this approach, some investigations (e.g. on portal vein and pulmonary artery) have shown a single store containing both RyR and IP 3 R, since depletion of the Ca 2+ store by caffeine (which activates RyR) prevented IP 3 -mediated Ca 2+ release [31,32,39,40]. On the other hand, other studies on pulmonary artery have suggested there may be separate stores for each receptor since depletion of the RyR-containing store did not abolish agonistevoked IP 3 -mediated Ca 2+ release and vice versa [41].…”

“…11.5). There may be multiple stores each containing both IP 3 R and RyR [28][29][30][31][32], or there may be stores which contain only RyR and separate stores only IP 3 R [12,28,[32][33][34] (e.g. basilar mesenteric or pulmonary arteries; Fig.…”