KN-62, a calcium calmodulin-dependent protein kinase II inhibitor, inhibits high potassium-stimulated prolactin secretion and intracellular calcium increases in anterior pituitary cells

In isolated rat anterior pituitary cells, KN-62 (10 mu M), an isoquinoline sulfonamide inhibitor of calcium/calmodulin-dependent protein kinase II, inhibited high KCl(50 mM)-stimulated prolactin secretion almost completely, with an IC50 of 95 nM. KN-62 inhibited TRH-induced prolactin secretion less effectively. KN-04, a compound that is over 100-fold less active in inhibiting purified calcium/calmodulin-dependent protein kinase II: also inhibited high KCl-stimulated prolactin secretion with an IC50 of 500 nM. KN-62 and KN-04 (10 mu M) both inhibited high KCl-stimulated increases in intracellular Ca2+ concentrations. We conclude that KN-62 and KN-04 inhibit activation of voltage-dependent calcium channels in anterior pituitary cells either directly or indirectly.