Module 7: Figure macula densa
Macula densa signal transduction mechanism.
Macula densa cells respond to an increase in the level of Na+ and Cl− in the lumen of the tubule by releasing ATP from the basolateral membrane. This ATP release through maxi-anion channels may be triggered by Ca2+, which may also act through phospholipase A2 (PLA2) to produce prostaglandin E2 (PGE2), which is released to stimulate the renin-producing granular cells. ATP functions to activate smooth muscle cells that control blood flow into the glomerulus and it can also be converted by ecto-ATPases into adenosine, which acts to inhibit renin secretion (Module 7: Figure renin secretion). NKCC2, Na+-K+-2Cl− cotransporter 2; SMCs, smooth muscle cells; PLA2, phospholipase A2.