Inhibitors of calmodulin-dependent protein kinase are nonspecific blockers of voltage-dependent K+ channels in vascular myocytes.
The present study was undertaken to investigate the effects of specific inhibitors of calmodulin-dependent protein kinase II (CamKII) on macroscopic voltage-dependent K(+) current (K(V)) recorded from rabbit portal vein smooth muscle cells. Inhibition of L-type Ca(2+) current facilitation by 1 microM KN-62, a blocker of CamKII, was first demonstrated and provided evidence for functional CamKII activity in this preparation. KN-93, another specific and more potent inhibitor of CamKII in the rat brain, suppressed K(V) and enhanced the rate of inactivation in a dose-dependent manner, in cells dialyzed with both low (0.1 mM) and high (10 mM) EGTA pipette solution. Prolonged dialysis with 10 microM of a synthetic peptide inhibitor of CamKII (fragment 281-301) had little effect on K(V) and did not prevent the inhibitory action of KN-93 on the current. The estimated IC(50) for inhibiting peak and late currents during 250-ms steps to +60 mV (holding potential = -60 mV) were 2.9 and 0.27 microM, respectively. KN-93 also induced slight shifts of the steady-state activation (-7 mV) and inactivation (-6 mV) curves. KN-62, and KN-92, an inactive analog of KN-93, produced effects similar to those of KN-93. In current clamp experiments, 5 microM KN-93 depolarized the myocytes from a control resting membrane potential of -42.3 +/- 2.8 mV to -28.5 +/- 1.4 mV, an effect that was partially reversible after washout (-34.4 +/- 1.3 mV, n = 6). In conclusion, blockers of CamKII produce nonspecific inhibitory effects on K(V) that warrant cautious use of these compounds in physiological experiments designed to assess the role of CamKII.
Ledoux
J
J
Department of Physiology, University of Montreal, and Research Centre, Montreal Heart Institute, Montreal, Canada.
Chartier
D
D
Leblanc
N
N
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology; D015220:Calcium Channels / Q000502:physiology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D011188:Potassium / Q000037:antagonists & inhibitors* / Q000502:physiology; D011817:Rabbits; D013449:Sulfonamides / Q000494:pharmacology; D000096926:Benzenesulfonamides
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D001596:Benzylamines; D002118:Calcium; D015220:Calcium Channels; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D011188:Potassium; D013449:Sulfonamides; C072105:KN 93; D000096926:Benzenesulfonamides; C063302:KN 62