A hypo-osmotically induced increase in intracellular Ca 2+ in lactating mouse mammary epithelial cells involving Ca 2+ influx

Abstract

Using a fluorescent Ca2+-sensitive dye, we studied the effect of hypo-osmotic stress on the intracellular free Ca2+ concentration ([Ca2+]i) in acini freshly isolated from lactating mouse mammary gland. The basal [Ca2+]i of mammary acini was unaffected by a 50% (v/v) dilution of suspensions with isotonic or hypertonic buffer, or after ionic (iso-osmotic) dilution (external Ca2+ was 3 mM). Hypo-osmotic dilution (50%) elicited a rapid increase in [Ca2+]i comprising a large, transient elevation, followed by a maintained plateau phase. No hypo-osmotically induced rise in [Ca2+]i was observed in the absence of extracellular Ca2+. Neither microtubule disassembly using nocodazole nor actin disruption with cytochalasin D prevented hypo-osmotically evoked stimulation of [Ca2+]i. Pre-incubation of acini with nifedipine did not prevent hypo-osmotically induced stimulation of [Ca2+]i, whereas a non-specific cation channel blocker, gadolinium, partially inhibited the increases in [Ca2+]i induced by hypo-osmotic stress. Furthermore, the transient component was still apparent, and not diminished in magnitude, after [Ca2+]i had been elevated by mobilisation of Ca2+ from intracellular stores using thapsigargin. The results demonstrate that hypo-osmotic stress generates an increase in [Ca2+]i in lactating mammary epithelial cells, the major, transient component of which appears to be due to influx of extracellular Ca2+.

Keratin mutations of epidermolysis bullosa simplex alter the kinetics of stress response to osmotic shock

“…An intact actin filament cytoskeleton appears to be required for activation of at least some of the volume regulatory mechanisms. Cell swelling requires actin mobilization and is accompanied by a calcium surge, either or both of which may be involved in the activation of membrane channels (Cornet et al, 1993;Foskett and Spring, 1985;Jessen and Hoffmann, 1992;Sudlow and Burgoyne, 1997). The resulting RVD response has been shown to be inhibited by both cytochalasin B (actin depolymerization) (Pedersen et al, 1999) and phalloidin (F-actin stabilization) (Shen et al, 1999).…”

Physiology of milk secretion

“…Milk can be stored for up to 48 h before the rate of milk synthesis and secretion begin to decrease. However, incomplete/inefficient milk removal or milk stasis induce multiple local effects on milk secretion: 1) an autocrine whey protein, termed 'feedback inhibitor of lactation' (FIL) regulates milk secretion according to frequency or completeness of milk removal in each MG [16]; 2) other factors such as osmolarity and mechanical stress [17] influence milk synthesis; 3) expression of the PRL receptors in MECs decreases, thereby uncoupling the stimulatory effects of PRL on milk synthesis; and 4) prolonged milk stasis triggers MECs apoptosis. Lactation is prolonged as long as milk is regularly removed from the MG [14].…”

Influence of Calcium on Regulatory Volume Decrease: Role of Potassium Channels

“…Inhibition of [Ca 2+ ] i increase during swelling by VACC blockers has been shown in rat pituitary GH3 cells [20], osteosarcoma UMR-106 cells [21], renal proximal tubule cells [19, 22, 23], IMCD cells [24], toad bladder cells [25], aorta smooth muscle [26], human fibroblasts [27], MTAL cells [28], newborn rat cardiomyocytes [29]and rat cortical astrocytes [30]. These channels appear not to be involved in Ca 2+ entry in cerebellar granule neurons and astrocytes [31, 32, 33], MDCK cells [34], urinary bladder epithelium [5], rabbit proximal tubule cells [35]and mammary epithelial cells [36]. In some cells, Ca 2+ entry is reduced by dihydropyridines but unaffected by other blockers with a general action on L-type VACC such as verapamil, diltiazem or Cd 2+ [17, 21].…”