Calsequestrin is a component of smooth muscles: the skeletal- and cardiac-muscle isoforms are both present, although in highly variable amounts and ratios.

摘要: Expression by smooth-muscle cells of calsequestrin (CS), the low-affinity/high-capacity Ca(2+)-binding protein striated-muscle sarcoplasmic reticulum (SR), has been investigated in recent years with conflicting results. Here we report purification and characterization from rat vas deferens two CS isoforms, first deemed skeletal muscle, second cardiac type, on account their N-terminal amino acids other relevant biochemical molecular properties. Compared deferens, smooth muscles aorta stomach, that order, were found to express lower amounts CS, whereas uterus bladder was not detectable. The ratio between isoforms also variable, stomach predominantly expressing skeletal-muscle type CSs roughly similar amount. Because property localize within SR lumen uniformly, but according distribution anchorage membrane proteins, expression suggests existence discrete endoplasmic-reticulum areas specialized rapidly exchanging Ca2+ storage release, thus control a variety functions, including contraction.