ATP-dependent calcium uptake into basolateral vesicles from transporting epithelia of intermolt crayfish

ATP-dependent Ca²⁺ uptake was determined into inside-out basolateral membrane vesicles (BLMV) from intermolt crayfish (Procambarus clarkii) Ca²⁺-transporting epithelia: gill, hepatopancreas (liver), and antennal gland (kidney). Extravesicular (EV) ATP (5 mM) increased ⁴⁵Ca²⁺ uptake (free Ca²⁺ 5 μM) by fivefold but was abolished by pretreatment with either vanadate or the ionophore A-23187. Addition of A-23187 to Ca²⁺-loaded vesicles produced 70% efflux. The saturable carrier exhibited a K(m) for Ca²⁺ of 0.11-0.27 μM and maxima] influx of 20-123 pmol · mg^-1 · min^{- 1}. The K(m) for ATP was 0.01-0.04 mM. The temperature coefficient ranged from 1.43 to 2.06. EGTA treatment of hepatopancreas and antennal gland vesicles decreased ⁴⁵Ca²⁺ uptake by 50-90%; uptake was restorable by calmodulin. However, in gill, ⁴⁵Ca²⁺ uptake was unaffected by EGTA treatment and calmodulin decreased uptake in both EGTA-treated and untreated vesicles. Addition of EV Na⁺ (5 mM) increased ATP-dependent Ca²⁺ uptake into hepatopancreas and antennal gland BLMV by 60%; in hepatopancreas BLMV, this increase was inhibitable by ouabain. However, ATP-dependent Ca²⁺ uptake in gill vesicles was Na⁺ independent. The relative role of each epithelium in whole animal Ca²⁺ homeostasis has been interpreted based on in vitro characteristics.