Calcium Channel Inhibitor, Verapamil, Inhibits the Voltage-Dependent K+ Channels in Rabbit Coronary Smooth Muscle Cells

Abstract

We investigated the effect of the phenylalkylamine Ca 2؉ ؉ channel inhibitor verapamil on voltage-dependent K ؉ ؉ (Kv) channels in rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Verapamil reduced the Kv current amplitude in a concentration-depenent manner. The apparent K d value for Kv channel inhibition was 0.82 m mM. Although verapamil had no effect on the activation kinetics, it accelerated the decay rate of Kv channel inactivation. The rate constants of association and dissociation by verapamil were 2.20؎ ؎0.02 m mM ؊ ؊1 s ؊ ؊1, and 1.79؎ ؎0.26 s ؊ ؊1, respectively. The steady-state activation and inactivation curves were unaffected by verapamil. The application of train pulses increased the verapamil-induced Kv channel inhibition. Furthermore, verapamil increased the recovery time constant, suggesting that the inhibitory effect of this agent was use-dependent. The inhibitory effect of verapamil was not affected by intracellular and extracellular Ca 2؉ ؉ -free conditions. Another Ca 2؉ ؉ channel inhibitor, nifedipine (10 m mM) did not affect the Kv current, and did not alter the inhibitory effect of verapamil. Based on these results, we concluded that verapamil inhibited Kv current in a state-, time-, and use-dependent manner, independent of Ca 2؉ ؉ channel inhibition.

The Effects of the Selective Serotonin Reuptake Inhibitor Fluvoxamine on Voltage-Dependent K⁺ Channels in Rabbit Coronary Arterial Smooth Muscle Cells

“…Several research groups, including ours, have attempted to identify the side effects of chemicals that affect vascularKvchannelsbesidestheirownfunction.Forexample, curcumin (spice), the phosphoinositide-3 kinase inhibitor LY294002, the L-type Ca 2+ channels inhibitor verapamil, the T-type Ca 2+ channels inhibitor mibefradil, the protein kinase C inhibitor bisindolylmaleimide (I), and the guanylyl cyclase activator YC-1 directly inhibited vascular Kv channels in the open state. [26][27][28][29][30][31] In addition, the Ca 2+ channels inhibitor efonidipine and NNC 55-0396, as well as the tyrosine kinase inhibitor genistein and the protein kinase A inhibitor H-89 directly inhibited the vascular Kv channel in the closed state. 13,14,32,33) Furthermore, our group also reported that the protein kinase C inhibitor staurosporine and the calmodulin inhibitor trifluoperazine inhibited the vascular Kv channel in both open and closed states.…”

The T-type Ca2+ Channel Inhibitor Mibefradil Inhibits Voltage-Dependent K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells

“…Similar effects have been reported for other ion channel activators/ inhibitors, independently of their own functions. For example, verapamil, a phenylalkylamine Ca 2+ channel inhibitor, directly inhibits Kv and BK Ca channels in vascular smooth muscle cells (30,31) and inhibited delayed rectifier K + current in cardiac myocytes (32,33). NS 1619 and BMS-204352, BK Ca channel activators, directly inhibited the cardiac L-type Ca 2+ channel (34,35).…”

Role of Calcium-Activated Potassium Channels in the Genesis of 3,4-Diaminopyridine-Induced Periodic Contractions in Isolated Canine Coronary Artery Smooth Muscles

“…The drugs that were used in the present study were: 1) inhibitors of calcium-activated-potassium channels (K Ca ); largeconductance K Ca inhibitors, iberiotoxin (IbTX; Sigma-Aldrich Japan, Tokyo, Japan) (Latorre et al, 1989;Marchenko and Sage, 1996); charybdotoxin (ChTX; Sigma-Aldrich Japan) (Miller et al, 1985); small-conductance K Ca inhibitor, apamine (Muraki et al, 1997); 2) CaCl 2 (Wako Pure Chemicals, Osaka, Japan); 3) inhibitors of L-type voltage-gated-calcium channels (Ca V ), nifedipine (Wako Pure Chemicals) (Medina et al, 2010), verapamil (Wako Pure Chemicals) (Ko et al, 2010); 4) agonist of L-type Ca V , Bay K8644 [S-(Ϫ)-1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl]phenyl)-3-pyridine carboxylic acid methyl ester] (Sigma-Aldrich Japan) (Amobi et al, 2010); 5) acidic and alkaline substances, HCl, lactic acid, NaOH, NaHCO 3 (Wako Pure Chemicals); 6) inhibitors of ion pumps: Na-pump (K ϩ -Na ϩ -ATPase) inhibitor, ouabain (Sigma-Aldrich Japan) (Briggs et al, 1996); 7) hybrid of ATP-sensitive potassium channel (K ATP ) opener and nitrate: nicorandil (Chugai Pharmaceutical Co, Tokyo, Japan) (Uchida et al, 1978;Yanagisawa et al, 1979); 8) K ATP opener, pinacidil (Wako Pure Chemicals) (Davies et al, 2010); 9) K ATP inhibitor, glibencramide (Wako Pure Chemicals) (Lindauer et al, 2003;Medina et al, 2010); 10) drugs that affect the sarcoplasmic reticulum (SR), caffeine (Wako Pure Chemicals) (Somlyo and Somlyo, 1976), dantrolene (Wako Pure Chemicals) (Kuba, 1980); 11) drugs that affect the mitochondria, oligomycin (Sigma-Aldrich Japan) (Visneskii et al, 1980); 12) ␤-adrenergic receptor agonist, isoproterenol (Sigma-Aldrich Japan) (Petkov and Nelson, 2005) Data Presentation. Because PCs of coronary artery rings obtained from the same beagle tend to provide a uniform response to a given stimulus (Uchida, 1985), each study group was composed of rings obtained from different beagles; therefore, the number of rings also indicated the number of beagles in the present study.…”