Spontaneous sarcoplasmic reticulum calcium release and extrusion from bovine, not porcine, coronary artery smooth muscle.

Abstract

SUMMARY1. We tested the hypothesis that the Ca2+-loaded sarcoplasmic reticulum (SR) of coronary artery smooth muscle spontaneously releases Ca2+ preferentially toward the sarcolemma to be extruded from the cell without increasing the average free myoplasmic [Ca2+] (Caim) concentration. 9. The results support the hypothesis that the SR spontaneously releases Ca2+ to be extruded from the cell. The species variation in the results may provide insight into the role of the SR as a Ca2' buffer barrier, which is sufficiently powerful to give rise to a restricted subsarcolemmal Ca2+ compartment in the resting cell.

Ca2+oscillations, gradients, and homeostasis in vascular smooth muscle

“…In the rabbit IVC, continuous unloading of the superficial SR to the extracellular space, involving coupling of SR release channels to the forward mode NCX, permits buffering of Ca 2ϩ influx to continue (51). Such spontaneous and preferential unloading of the SR toward the PM has also been observed in the bovine coronary artery (65). In support of this postulate, Fig.…”

Pharmacological Modulation of Sarcoplasmic Reticulum Function in Smooth Muscle

“…Also, [Ca 2ϩ ] cyt reported by FFP-18 reaches levels about 3 times higher than that reported by fura-2. In freshly isolated bovine, porcine, and guinea pig coronary artery smooth muscle cells (Stehno-Bittel and Sturek, 1992;Ganitkevich, 1996), the K Ca -mediated current was used to report subplasmalemmal [Ca 2ϩ ] cyt . It was monitored simultaneously with fura-2 "global" [Ca 2ϩ ] cyt signals.…”

“…This large cell surface/cell volume ratio in smooth muscle favors exquisite regulation of cell surface processes by instantaneous changes in intracellular composition, such as the regulation by (presumably) spontaneously released Ca 2ϩ from the SR, known as "Ca 2ϩ sparks", of Ca 2ϩ -activated K ϩ (K Ca ) (see reviews by Wellman and Nelson, 2003) and chloride (Cl Ca ) channels (Kotlikoff and Wang, 1998). Earlier studies by Benham and Bolton (1986) and by Stehno-Bittel and Sturek (1992) lead to the suggestion that the frequently observed spontaneous K ϩ currents recorded in smooth muscle (Benham and Bolton, 1986;Ohya et al, 1987;Desilets et al, 1989;Hume and Leblanc, 1989) occur in regions of the cell where the SR and the PM are closely apposed. This Ca 2ϩ release from the SR, presumed to occur spontaneously, occurs in close proximity to K Ca channels and reaches a [Ca 2ϩ ] cyt of 10 to 100 M and an average size of 13 m 2 , which covers ϳ1% of the 1300 m 2 of the smooth muscle membrane .…”

Spontaneous Ca2+ oscillations in subcellular compartments of vascular smooth muscle cells rely on different Ca2+ pools

“…Ten years ago, we demonstrated significant non-uniformity in the distribution of Ca 2+ in quiescent vascular smooth muscle cells using patch-clamp and microscopy techniques [16,17]. Since then, several reports have demonstrated that non-uniform Ca 2+ distribution exists in smooth muscle cells in a variety of conditions [1,18,19].…”