scholarly journals The Influence of Sarcoplasmic Reticulum Ca2+ Concentration on Ca2+ Sparks and Spontaneous Transient Outward Currents in Single Smooth Muscle Cells

1999 ◽  
Vol 113 (2) ◽  
pp. 215-228 ◽  
Author(s):  
Ronghua ZhuGe ◽  
Richard A. Tuft ◽  
Kevin E. Fogarty ◽  
Karl Bellve ◽  
Fredric S. Fay ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Potassium Channels ◽  
Smooth Muscle Cells ◽  
High Speed ◽  
Muscle Cells ◽  
Wide Field ◽  
Outward Currents ◽  
The Relationship ◽  
Spontaneous Transient Outward Currents

Localized, transient elevations in cytosolic Ca2+, known as Ca2+ sparks, caused by Ca2+ release from sarcoplasmic reticulum, are thought to trigger the opening of large conductance Ca2+-activated potassium channels in the plasma membrane resulting in spontaneous transient outward currents (STOCs) in smooth muscle cells. But the precise relationships between Ca2+ concentration within the sarcoplasmic reticulum and a Ca2+ spark and that between a Ca2+ spark and a STOC are not well defined or fully understood. To address these problems, we have employed two approaches using single patch-clamped smooth muscle cells freshly dissociated from toad stomach: a high speed, wide-field imaging system to simultaneously record Ca2+ sparks and STOCs, and a method to simultaneously measure free global Ca2+ concentration in the sarcoplasmic reticulum ([Ca2+]SR) and in the cytosol ([Ca2+]CYTO) along with STOCs. At a holding potential of 0 mV, cells displayed Ca2+ sparks and STOCs. Ca2+ sparks were associated with STOCs; the onset of the sparks coincided with the upstroke of STOCs, and both had approximately the same decay time. The mean increase in [Ca2+]CYTO at the time and location of the spark peak was ∼100 nM above a resting concentration of ∼100 nM. The frequency and amplitude of spontaneous Ca2+ sparks recorded at −80 mV were unchanged for a period of 10 min after removal of extracellular Ca2+ (nominally Ca2+-free solution with 50 μM EGTA), indicating that Ca2+ influx is not necessary for Ca2+sparks. A brief pulse of caffeine (20 mM) elicited a rapid decrease in [Ca2+]SR in association with a surge in [Ca2+]CYTO and a fusion of STOCs, followed by a fast restoration of [Ca2+]CYTO and a gradual recovery of [Ca2+]SR and STOCs. The return of global [Ca2+]CYTO to rest was an order of magnitude faster than the refilling of the sarcoplasmic reticulum with Ca2+. After the global [Ca2+]CYTO was fully restored, recovery of STOC frequency and amplitude were correlated with the level of [Ca2+]SR, even though the time for refilling varied greatly. STOC frequency did not recover substantially until the [Ca2+]SR was restored to 60% or more of resting levels. At [Ca2+]SR levels above 80% of rest, there was a steep relationship between [Ca2+]SR and STOC frequency. In contrast, the relationship between [Ca2+]SR and STOC amplitude was linear. The relationship between [Ca2+]SR and the frequency and amplitude was the same for Ca2+ sparks as it was for STOCs. The results of this study suggest that the regulation of [Ca2+]SR might provide one mechanism whereby agents could govern Ca2+ sparks and STOCs. The relationship between Ca2+ sparks and STOCs also implies a close association between a sarcoplasmic reticulum Ca2+ release site and the Ca2+-activated potassium channels responsible for a STOC.

Ca2+ spark sites in smooth muscle cells are numerous and differ in number of ryanodine receptors, large-conductance K+ channels, and coupling ratio between them

2004 ◽  
Vol 287 (6) ◽  
pp. C1577-C1588 ◽  
Author(s):  
Ronghua ZhuGe ◽  
Kevin E. Fogarty ◽  
Stephen P. Baker ◽  
John G. McCarron ◽  
Richard A. Tuft ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
High Speed ◽  
Ryanodine Receptors ◽  
Muscle Cells ◽  
Bk Channels ◽  
Wide Field ◽  
Coupling Ratio ◽  
Patch Clamp Recording ◽  
High Speed Imaging

Ca2+ sparks are highly localized Ca2+ transients caused by Ca2+ release from sarcoplasmic reticulum through ryanodine receptors (RyR). In smooth muscle, Ca2+ sparks activate nearby large-conductance, Ca2+-sensitive K+ (BK) channels to generate spontaneous transient outward currents (STOC). The properties of individual sites that give rise to Ca2+ sparks have not been examined systematically. We have characterized individual sites in amphibian gastric smooth muscle cells with simultaneous high-speed imaging of Ca2+ sparks using wide-field digital microscopy and patch-clamp recording of STOC in whole cell mode. We used a signal mass approach to measure the total Ca2+ released at a site and to estimate the Ca2+ current flowing through RyR [ ICa(spark)]. The variance between spark sites was significantly greater than the intrasite variance for the following parameters: Ca2+ signal mass, ICa(spark), STOC amplitude, and 5-ms isochronic STOC amplitude. Sites that failed to generate STOC did so consistently, while those at the remaining sites generated STOC without failure, allowing the sites to be divided into STOC-generating and STOC-less sites. We also determined the average number of spark sites, which was 42/cell at a minimum and more likely on the order of at least 400/cell. We conclude that 1) spark sites differ in the number of RyR, BK channels, and coupling ratio of RyR-BK channels, and 2) there are numerous Ca2+ spark-generating sites in smooth muscle cells. The implications of these findings for the organization of the spark microdomain are explored.

Oxygen-induced fetal pulmonary vasodilation is mediated by intracellular calcium activation of KCa channels

2001 ◽  
Vol 281 (6) ◽  
pp. L1379-L1385 ◽  
Author(s):  
Valerie A. Porter ◽  
Michael T. Rhodes ◽  
Helen L. Reeve ◽  
David N. Cornfield
Keyword(s):  
Smooth Muscle ◽  
Pulmonary Artery ◽  
Smooth Muscle Cells ◽  
Intracellular Calcium ◽  
Muscle Cells ◽  
Pulmonary Vasodilation ◽  
Outward Currents ◽  
Acute Increase ◽  
Pulmonary Artery Smooth Muscle ◽  
Spontaneous Transient Outward Currents

O2 sensing in fetal pulmonary artery smooth muscle is critically important in the successful transition to air breathing at birth. However, the mechanism by which the fetal pulmonary vasculature senses and responds to an acute increase in O2tension is not known. Isolated fetal pulmonary artery smooth muscle cells were kept in primary culture for 5–14 days in a hypoxic environment (20–30 mmHg). These cells showed a 25.1 ± 1.7% decrease in intracellular calcium in response to an acute increase in O2 tension. Low concentrations of caffeine (0.5 mM) and diltiazem also decreased intracellular calcium. The decrease in intracellular calcium concentration in response to increasing O2 was inhibited by iberiotoxin and ryanodine. Freshly isolated fetal pulmonary artery smooth muscle cells exhibited “spontaneous transient outward currents,” indicative of intracellular calcium spark activation of calcium-sensitive potassium channels. The frequency of spontaneous transient outward currents increased when O2 tension was increased to normoxic levels. Increasing fetal pulmonary O2 tension in acutely instrumented fetal sheep increased fetal pulmonary blood flow. Ryanodine attenuated O2-induced pulmonary vasodilation. This study demonstrates that fetal pulmonary vascular smooth muscle cells are capable of responding to an acute increase in O2tension and that this O2 response is mediated by intracellular calcium activation of calcium-sensitive potassium channels.

Inhibition of SERCA pumps induces desynchronized RyR activation in overloaded internal Ca2+ stores in smooth muscle cells

2010 ◽  
Vol 298 (5) ◽  
pp. C1038-C1046 ◽  
Author(s):  
Norma Leticia Gómez-Viquez ◽  
Guadalupe Guerrero-Serna ◽  
Fernando Arvizu ◽  
Ubaldo García ◽  
Agustín Guerrero-Hernández
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Smooth Muscle Cells ◽  
Ryanodine Receptors ◽  
Muscle Cells ◽  
Local Communication ◽  
Outward Currents ◽  
Serca Pump

We have previously shown that rapid inhibition of sarcoplasmic reticulum (SR) ATPase (SERCA pumps) decreases the amplitude and rate of rise (synchronization) of caffeine induced-Ca2+ release without producing a reduction of free luminal SR Ca2+ level in smooth muscle cells (Gómez-Viquez L, Guerrero-Serna G, García U, Guerrero-Hernández A. Biophys J 85: 370–380, 2003). Our aim was to investigate the role of luminal SR Ca2+ content in the communication between ryanodine receptors (RyRs) and SERCA pumps. To this end, we studied the effect of SERCA pump inhibition on RyR-mediated Ca2+ release in smooth muscle cells with overloaded SR Ca2+ stores. Under this condition, the amplitude of RyR-mediated Ca2+ release was not affected but the rate of rise was still decreased. In addition, the caffeine-induced Ca2+-dependent K+ outward currents revealed individual events, suggesting that SERCA pump inhibition reduces the coordinated activation of RyRs. Collectively, our results indicate that SERCA pumps facilitate the activation of RyRs by a mechanism that does not involve the regulation of SR Ca2+ content. Importantly, SERCA pumps and RyRs colocalize in smooth muscle cells, suggesting a possible local communication between these two proteins.

scholarly journals Regulation of Calcium Sparks and Spontaneous Transient Outward Currents by RyR3 in Arterial Vascular Smooth Muscle Cells

2001 ◽  
Vol 89 (11) ◽  
pp. 1051-1057 ◽  
Author(s):  
Matthias Löhn ◽  
Wolfgang Jessner ◽  
Michael Fürstenau ◽  
Maren Wellner ◽  
Vincenzo Sorrentino ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Muscle Cells ◽  
Calcium Sparks ◽  
Outward Currents ◽  
Spontaneous Transient Outward Currents
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