Submitted on February 18, 2007
Accepted on August 9, 2007
P2Y Receptor Regulation of Sodium Transport in Human Mammary Epithelial Cells
So Yeong Lee1, Melissa L. Palmer2, Peter J. Maniak3, Soo Hwa Jang1, Pan Dong Ryu1, and Scott M. O'Grady4*
1 Department of Veterinary Pharmacology, College of Veterinary Medicine, Seoul National University, Seoul, Korea, Republic of
2 Biology, University of Minnesota, St. Paul, Minnesota, United States
3 Physiology, University of Minnesota, St. Paul, Minnesota, United States
4 St. Paul, Minnesota, United States; Physiology, University of Minnesota, St. Paul, Minnesota, United States
* To whom correspondence should be addressed. E-mail: ograd001{at}umn.edu.
Primary mammary epithelial cells (HME cells) were immortalized by stable, constitutive expression of the catalytic subunit of human telomerase (hTERT). Purinergic receptors were identified by RT-PCR and quantitative RT-PCR from mRNA isolated from primary and immortalized cells. Several subtypes of P2Y receptor mRNA were identified including P2Y1, P2Y2, P2Y4 and P2Y6 receptors. Confluent monolayers of HME cells exhibited a basal short circuit current (Isc) that was abolished by amiloride and benzamil. When monolayers were cultured in the presence of hydrocortisone, mRNA expression of 
, 
and 
Na channel (ENaC) subunits increased 3 fold and basal benzamil-sensitive Na+ transport increased nearly 2 fold. Stimulation with UTP, UDP and ATP--S each produced increases in intracellular calcium concentration ([Ca2+]i) that was inhibited if the cells were pretreated with BAPTA-AM. The rank order of potency for these P2Y receptor agonists was UTP>UDP>ATP--S. Basolateral UTP stimulation produced a rapid increase in Isc that was significantly blocked following pretreatment with BAPTA-AM. Moreover, basolateral charybdotoxin or clotrimazole significantly inhibited the UTP-stimulated Isc. These results indicated that HME cells express multiple P2 receptors and that Ca2+ mobilization evoked by UTP stimulates Na+ absorption by increasing the activity of basolateral Ca2+-activated K+ channels.
