scholarly journals Release and recycling of calcium by the sarcoplasmic reticulum in guinea-pig portal vein smooth muscle.

1984 ◽  
Vol 355 (1) ◽  
pp. 677-695 ◽  
Author(s):  
M Bond ◽  
T Kitazawa ◽  
A P Somlyo ◽  
A V Somlyo
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Portal Vein

scholarly journals Freeze-fracture studies of nexuses between smooth muscle cells. Close relationship to sarcoplasmic reticulum.

1977 ◽  
Vol 72 (1) ◽  
pp. 26-34 ◽  
Author(s):  
G N Fry ◽  
C E Devine ◽  
G Burnstock
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Hexagonal Lattice ◽  
Freeze Fracture ◽  
Minimum Size ◽  
Mouse Vas Deferens ◽  
Chicken Gizzard ◽  
Close Relationship ◽  
Fracture Appearance

The freeze-fracture appearance of the nexus was compared in the smooth muscle of guinea pig sphincter pupillac, portal vein, pulmonary artery, taenia coli, uretzr, and vas diferens, mouse vas deferens, chicken gizzard and anterior mesenteric artery, and toad stomach. Nexuses are particularly numerous in the guinea pig sphincter pupillae; they are usually oval and their average area is 0.15 mum2, although some as large as 0.6 mum2 were seen. Small aggregations of particles were observed which would not be recognizable as nexuses in thin section. What constitutes the minimum size of a nexus is discussed. It is estimated that the number of nexuses per cell in this preparation is of the order of tens rather than hundreds. All nexuses examined had 6-9-nm particles in the PF face, with corresponding 3-4-nm pits on the EF face forming a polygonal tending towards a hexagonal lattice. The nexuses are arranged in rows parallel to the main axis of the cell, usually alternating with longitudinal rows of plasmalemmal vesicles. Many nexuses in the guinea pig sphincter pupillae, chicken gizzard, and toad stomach show a close relationship with sarcoplasmic reticulum. The possibility that this may have some role in current flow across this specialized junction is discussed.

Inositol 1,4,5-trisphosphate receptors modulate Ca2+ sparks and Ca2+ store content in vas deferens myocytes

2003 ◽  
Vol 285 (1) ◽  
pp. C195-C204 ◽  
Author(s):  
Carl White ◽  
J. Graham McGeown
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Vas Deferens ◽  
Confocal Imaging ◽  
Time Duration ◽  
Outward Currents ◽  
Inositol 1,4,5 Trisphosphate ◽  
Dependent Pathway ◽  
Spontaneous Transient Outward Currents

Spontaneous Ca2+ sparks were observed in fluo 4-loaded myocytes from guinea pig vas deferens with line-scan confocal imaging. They were abolished by ryanodine (100 μM), but the inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) blockers 2-aminoethoxydiphenyl borate (2-APB; 100 μM) and intracellular heparin (5 mg/ml) increased spark frequency, rise time, duration, and spread. Very prolonged Ca2+ release events were also observed in ∼20% of cells treated with IP3R blockers but not under control conditions. 2-APB and heparin abolished norepinephrine (10 μM; 0 Ca2+)-evoked Ca2+ transients but increased caffeine (10 mM; 0 Ca2+) transients in fura 2-loaded myocytes. Transients evoked by ionomycin (25 μM; 0 Ca2+) were also enhanced by 2-APB. Ca2+ sparks and transients evoked by norepinephrine and caffeine were abolished by thimerosal (100 μM), which sensitizes the IP3R to IP3. In cells voltage clamped at –40 mV, spontaneous transient outward currents (STOCs) were increased in frequency, amplitude, and duration in the presence of 2-APB. These data are consistent with a model in which the Ca2+ store content in smooth muscle is limited by tonic release of Ca2+ via an IP3-dependent pathway. Blockade of IP3Rs elevates sarcoplasmic reticulum store content, promoting Ca2+ sparks and STOC activity.

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