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Articles in PresS, published online ahead of print November 27, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00238.2002
Submitted on May 22, 2002
Accepted on November 22, 2002
1 Molecular and Cell Biology, UC Berkeley, Berkeley, CA, USA
2 Molecular and Cell Biology, UC Berkeley, Berkeley, CA, USA; School of Optometry, UC Berkeley, Berkeley, CA, USA
* To whom correspondence should be addressed. E-mail: smiller{at}socrates.berkeley.edu.
It has been reported that secretory mammary epithelia cells (MEC) release ATP, UTP and UDP upon mechanical stimulation. Here we examined the physiological changes caused by ATP/UTP in non-transformed, clonal mouse mammary epithelia (31EG4 cells). In control conditions, transepithelial potential (apical side negative) and resistance were - 4.4 ± 1.3 mV (mean ± SD, n=12) and 517.7 ± 39.4 
x cm2, respectively. The apical membrane potential was - 43.9 ± 1.7 mV and the ratio of apical to basolateral membrane resistance (RA/RB) was 3.5 ± 0.2. Addition of ATP or UTP to the apical or basolateral membranes caused large voltage and resistance changes with an EC50 of ~ 24 µM (apical) and ~ 30 µM (basal). Apical ATP/UTP (100 µM) depolarized VA by 17.6 ± 0.8 mV (n = 7) and decreased RA/RB by a factor of ~ 3. The addition of adenosine to either side (100 µM) had no effect on any of these parameters. The ATP/UTP responses were partially inhibited by DIDS and suramin and mediated by a transient increase in free [Ca2+]in, 427 ± 206 nM (15-25 µM ATP, apical; n = 6). This calcium increase was blocked by cyclopiazonic acid, by BAPTA or by xestospongin C. 31EG4 MEC monolayers also secreted or absorbed fluid in the resting state, and ATP or UTP increased fluid secretion by 5.6 ± 3 µl x cm-2 x hr-1 (n = 10). Pharmacology experiments indicate that 31EG4 epithelia contain P2Y2 purinoceptors on the apical and basolateral membranes, which upon activation stimulate apical calcium-dependent chloride channels and cause fluid secretion across the monolayer. This suggests that extracellular nucleotides could play a fundamental role in mammary gland paracrine signaling and the regulation of milk composition in vivo.
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