Macula Densa!!

just copied this from pubmed. but this seems a nice article.

Macula densa cells are unique renal biosensor cells that detect changes in luminal NaCl concentration ([NaCl]_L) and transmit signals to the mesangial cell/afferent arteriolar complex. They are the critical link between renal salt and water excretion and glomerular hemodynamics, thus playing a key role in regulation of body fluid volume. Since identification of these cells in the early 1900s, the nature of the signaling process from macula densa cells to the glomerular contractile elements has remained unknown. In patch–clamp studies of macula densa cells, we identified an [NaCl]_L-sensitive ATP-permeable large-conductance (380 pS) anion channel. Also, we directly demonstrated the release of ATP (up to 10 μM) at the basolateral membrane of macula densa cells, in a manner dependent on [NaCl]_L, by using an ATP bioassay technique.

url : http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12655045