Vats J. Properties of Ca2+ pumps of acinar secretory cells from rats submandibular salivary gland.

Dissertation is devoted to the study of the properties of plasma and endoplasmic reticulum membranes Ca2+-activated Mg2+-dependent ATPases of rat submandibular salivary gland cells. In the experiments using isolated acini secretory cells was shown that intracellular Ca2+ homeostasis and spontaneous secretion are maintained by coordinated functioning of both Ca2+ pumps and plasma membrane channels. We showed that integral fraction of inside-out oriented membrane vesicles is enriched with thapsigargin-insensitive plasma membrane Ca2+-ATPase and thapsigargin-sensitive endoplasmic reticulum Ca2+-ATPase molecules. High- and low-affinity ATP- and Ca2+-binding sites in the molecules of plasma and endoplas-mic reticulum membranes Ca2+-ATPases were revealed. The ability of other bivalent metal cations and nucleotides to suppress the activity of plasma and endoplasmic reticulum membrane Ca2+-ATPases de-creased in the following sequences: Са2+=Ba2+>Sr2+ and Са2+=Ba2+=Sr2+; Mg2+>Mn2+>Co2+>Cu2+ and Mg2+=Mn2+>Cu2+>Co2+; ATP>GTP>UTP>CTP and ATP>GTP>CTP>UTP correspondingly. Plasma and endoplasmic reticulum membrane Ca2+-ATPases are inhibited by eosin Y>p-chloromercuribenzoate>La3+. It was found that in the regulation of both Ca2+-ATPases important role belong to imidazole group of histidine and SH-group of cysteine consisting of ATP-binding sites.