Hypo-osmolality activates IK_Ca.

A: Relationship between ⁸⁶Rb efflux and extracellular fluid osmolality in multinucleated cytotrophoblasts at 66 h culture. The cells were bathed in Tyrode’s buffer with an osmolality of 283 (control), 218, 183 or 138 mOsm/kgH₂O (shown in italics) for 10 min and the total ⁸⁶Rb efflux over this period was plotted against 1/osmolality. Values are mean ± SE (n = 4–5 placentas); *p<0.001 vs. control at 66 h in culture; ANOVA with Turkey Kramer multicomparison post hoc test. B-D: Characterization of swelling-activated ⁸⁶Rb efflux in multinucleated cytotrophoblasts (66 h). Time course of %⁸⁶Rb efflux over 13 min; during the experimental period (indicated by the bar) cells were (B) untreated (control) or exposed to hyposmotic solution (145 mOsm/kgH₂O) or Ca²⁺-free hyposmotic (n = 6 placentas); (C) control, hyposmotic solution or hyposmotic solution+TRAM-34 (n = 5 placentas); (D) hyposmotic solution, hyposmotic solution+apamin or hyposmotic solution+charybdotoxin (ChTx) (n = 5 placentas). Data are mean ± SE.