A hypo-osmotically induced increase in intracellular Ca2+ in lactating mouse mammary epithelial cells involving Ca2+ influx.
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+.
Sudlow
A W
AW
The Physiological Laboratory, University of Liverpool, PO Box 147, Liverpool L69 3BX, UK.
Burgoyne
R D
RD
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2; D007774:Lactation; D008321:Mammary Glands, Animal / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D009994:Osmolar Concentration
D005456:Fluorescent Dyes; D002118:Calcium; D016257:Fura-2