Superficial buffer barrier

Turner WH, Brading AF 1997 Smooth muscle of the bladder in the normal and the diseased state pathophysiology, diagnosis and treatment. Pharmacol Ther 75 77—110 van Breemen C, Chen Q, Laher I 1995 Superficial buffer barrier function of smooth muscle sarcoplasmic reticulum. Trends Pharmacol Sci 16 98-105 Wray S 1993 Uterine contraction and physiological mechanisms of modulation. Am J Physiol 264 C1-C18... 

FIG. 5. Maintenance of the superficial buffer barrier depends on NCX-assisted Ca2+ transport from the SR lumen to the extracellular space. (A) Rate of loss of SR Ca2+ content, measured as a caffeine transient, into Ca2+ free perfusate at room temperature. (B) Rate of decline in [Ca2+ I from an elevated level, measured as fura 2 fluorescence ratio, into Ca2+ free superfusate, which is either Na+ free or contains 10 /rM CPA or is Na+ free and contains CPA. (C) This cartoon represents a model for maintained buffering by the superficial SR of Ca2+ entry. Ca2+ taken up by SERCA is subsequently released into the SR-PM junctional space from where it is extruded by the NCX. 

Carafoli E, Santella L, Branca D, Brini M 2001 Generation, control, and processing of cellular calcium signals. Crit Rev Biochem Mol Biol 36 107—260 Chen Q, van Breemen C 1993 The superficial buffer barrier in venous smooth muscle sarcoplasmic reticulum refilling and unloading. Br J Pharmacol 109 336—343 Clapham DE, Runnels LW, Strubing C 2001 The TRP ion channel family. Nat Rev Neurosci 2 387-396... 

Janssen LJ, Betti PA, Netherton SJ, Walters DK 1999 Superficial buffer barrier and preferentially directed release of Ca2+ in canine airway smooth muscle. 7km J Physiol 276 L744—L753... 

In addition to this function of controlling the overall cytosolic Ca " concentration adjacent to the myofilaments in the deep cytosol, there is evidence that the st also plays a role in controlling the influx of extracellular Ca -" through the plasmalemmal membrane. This has led to the independent proposal of two concepts - the superficial buffer barrier hypothesis and the capacita-tive model - both of which attempt to link sr function to extracellular Ca " influx. 

Chen, Q., Cannell, M. and Van Breemen, C. (1992). The superficial buffer barrier in vascular smooth muscle. Can. J. Physiol. Pharmacol. 70(4), 509-514. 

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