Jae-Hong Ko

Staurosporine inhibits voltage-dependent K+ current through a PKC-independent mechanism in isolated coronary arterial smooth muscle cells.

We examined the effects of the protein kinase C (PKC) inhibitor staurosporine (ST) on voltage-dependent K+ (KV) channels in rabbit coronary arterial smooth muscle cells. ST inhibited the KV current in a dose-dependent manner with a Kd value of 1.3 μM. The inhibition of the KV current by ST was voltage-dependent between −30 and +10 mV. The additive inhibition of the KV current by ST was voltage-dependent throughout the activation voltage range. The rate constants of association and dissociation of ST were 0.63 μM−1 s−1 and 0.92 s−1, respectively. ST produced use-dependent inhibition of the KV current. ST shifted the activation curve to more positive potentials but did not have any significant effect on the voltage dependence of the inactivation curve. ST did not have any significant effects on other types of K+ channel. Another PKC inhibitor, chelerythrine, and PKA inhibitor peptide (PKA-IP) had little effect on the KV current. These results suggest that ST interacts with KV channels that are in the closed state and that ST inhibits KV channels in the open state in a manner that is phosphorylation-independent and voltage-, time-, and use-dependent.

Endothelin-1 inhibits inward rectifier K+ channels in rabbit coronary arterial smooth muscle cells through protein kinase C.

We studied inward rectifier K+ (Kir) channels in smooth muscle cells isolated from rabbit coronary arteries. In cells from small- (<100 μm, SCASMC) and medium-diameter (100 ∼ 200 μm, MCASMC) coronary arteries, Kir currents were clearly identified (11.2 ± 0.6 and 4.2 ± 0.6 pA pF−1 at -140 mV in SCASMC and MCASMC, respectively) that were inhibited by Ba2+ (50 μM). By contrast, a very low Kir current density (1.6 ± 0.4 pA pF−1) was detected in cells from large-diameter coronary arteries (>200 μm, LCASMC). The presence of Kir2.1 protein was confirmed in SCASMC in a Western blot assay. Endothelin-1 (ET-1) inhibited Kir currents in a dose-dependent manner. The inhibition of Kir currents by ET-1 was abolished by pretreatment with the protein kinase C (PKC) inhibitor staurosporine (100 nM) or GF 109203X (1 μM). The PKC activators phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acetyl-sn-glycerol (OAG) reduced Kir currents. The ETA-receptor inhibitor BQ-123 prevented the ET-1-induced inhibition of Kir currents. The amplitudes of the ATP-dependent K+ (KATP), Ca2+-activated K+ (BKCa), and voltage-dependent K+ (KV) currents, and effects of ET-1 on these channels did not differ between SCASMC and LCASMC. From these results, we conclude that Kir channels are expressed at a higher density in SCASMC than in larger arteries and that the Kir channel activity is negatively regulated by the stimulation of ETA-receptors via the PKC pathway.

Increased Inhibition of Inward Rectifier K+ Channels by Angiotensin II in Small-Diameter Coronary Artery of Isoproterenol-Induced Hypertrophied Model

Objective—We investigated the effects of angiotensin II (Ang II) on inward rectifier K+ (Kir) channels in small-diameter coronary arterial smooth muscle cells (SCASMCs) of control and isoproterenol (Iso)-induced hypertrophied rabbits. Methods and Results—Kir current amplitude and Kir channel protein expression were definitely lower in the Iso-induced hypertrophied model than in the control. In a pressurized arterial experiment, 15 mmol/L K+-induced vasodilation was greater in the control arteries than in the arteries of Iso-induced hypertrophied model. Ang II reduced the Kir current in a concentration-dependent manner, and this inhibition was greater in SCASMCs from Iso-induced hypertrophied model than from control. Although, there was no difference in the expression of Ang II type 2 (AT2) receptor between SCASMCs of control and Iso-induced hypertrophied model, the expression of Ang II type 1 (AT1) receptor and phosphorylated PKCα were greater in SCASMCs of Iso-induced hypertrophied model than of control. Conclusion—Ang II inhibits Kir channels more prominently in SCASMCs of Iso-induced hypertrophied model owing to increases in the expression of AT1 receptor and the activation of PKCα. Our findings about the differential expression of Kir channels and different modulation of Kir channels by a vasoconstrictor (Ang II) in a hypertrophy model are important for better understanding the responsiveness of small-diameter arteries during hypertrophy.