INHIBITION OF VOLTAGE-GATED CA2-CELL LUNG-CARCINOMA BY THE CA2+( CHANNEL ACTIVITY IN SMALL)CALMODULIN-DEPENDENT PROTEIN-KINASE INHIBITOR KN-62 SULFONYL)-N-METHYL-L-TYROSYL]-4-PHENYLPIPERAZINE)/

Although small cell lung carcinoma (SCLC) cells express both voltage-g ated Ca2+ channels (VGCC) and second messenger-operated Ca2+ channels (SMOCC), little is known about the factors that regulate the activity of these channels in SCLC cells. Ca2+/calmodulin-dependent protein kin ase (CaM kinase) type II has been implicated recently in regulating Ca 2+ channel activity in other cell types. Because of this, we investiga ted the effects of the specific CaM kinase antagonist nesulfonyl)-N-me thyl-L-tryosyl]-4-phenylpiperazine (KN-62) on Ca2+ channel activity in SCLC cells. Incubation with 10 mu M KN-62 for 20 min inhibited depola rization-dependent Ca-45(2+) influx by 96.1 +/- 2.1% in four independe nt SCLC cell lines, and by 42.2 +/- 6.8% in the NCI-H146 SCLC cell lin e. Similar inhibitory effects of KN-62 were observed when Fura-2 was u sed to measure depolarization-dependent Ca2+ influx. These results ind icate that KN-62 potently inhibits VGCC activity in SCLC cells. In con trast, KN-62 (10 mu M, 20 min) did not inhibit significantly Ca2+ mobi lization induced by muscarinic acetylcholine receptor (mAChR) activati on in SCLC cells. This indicates that SMOCC are less susceptible than VGCC to inhibition by KN-62 in SCLC cells. Because mAChR activation al so inhibits VGCC activity in SCLC cells, we examined the effects of KN -62 on the mAChR-mediated inhibition of VGCC activity. To do this, we measured depolarization-dependent Ca-45(2+) influx in SCLC cells incub ated with submaximal concentrations of KN-62 and the mAChR agonist car bachol. Treatment of cells with both drugs resulted in almost twice as much inhibition of VGCC activity as in cells treated with only one of the drugs. This indicates that inactivation of CaM kinase with KN-62 does not suppress the ability of mAChR agonists to inhibit VGCC activi ty.