The Effect of Midazolam on Outward K+ Channel Currents in Rabbit Cerebral Arterial Smooth Muscle Cells / 대한마취과학회지

BACKGROUND: Midazolam has a direct relaxing effect on vascular smooth muscle, but the mechanisms that this agent produces muscle relaxation are not fully understood. The current study was performed to identify the effects of the midazolam on K+ channels current in rabbit cerebral arterial smooth muscle cells. METHODS: Whole cell patch-clamp recording technique was used to evaluate the effects of midazolam (0.1 to 100micrometer) on outward K+ channel currents in dispersed rabbit cerebral arterial smooth muscle cells. RESULTS: Outward K+ currents of rabbit cerebral artery smooth muscle cells were voltage-dependent. Midazolam (10, 100micrometer) tested significantly inhibited outward K+ currents in a dose-dependent manner and half-blocking concentration (IC50) was 15.94micrometer at 60 mV. CONCLUSIONS: Midazolam inhibit outward K+ currents of rabbit cerebral arterial smooth muscle cells. Further study will be needed to determine the effect of midazolam on calcium channel current because it is unclear if the inhibitory effect of midazolam on outward K+current induces vasoconstriction.

Decreased voltage dependent K+ currents in cerebral arterial smooth muscle cells of one-kidney, one-clip Goldblatt hypertensive rat

The Kv channel activity in vascular smooth muscle cell plays an important role in the regulation of membrane potential and blood vessel tone. It was postulated that increased blood vessel tone in hypertension was associated with alteration of Kv channel and membrane potential. Therefore, using whole cell mode of patch-clamp technique, the membrane potential and the 4-AP-sensitive Kv current in cerebral arterial smooth muscle cells were compared between normotensive rat and one-kidney, one-clip Goldblatt hypertensive rat (1K,1C-GBH rat). Cell capacitance of hypertensive rat was similar to that of normotensive rat. Cell capacitance of normotensive rat and 1K,1C-GBH rat were 20.8+/-2.3 and 19.5+/-1.4 pF, respectively. The resting membrane potentials measured in current clamp mode from normotensive rat and 1K,1C-GBH rat were -45.9+/-1.7 and -38.5+/-1.6 mV, respectively. 4-AP (5 mM) caused the resting membrane potential hypopolarize but charybdotoxin (0.1 muM) did not cause any change of membrane potential. Component of 4-AP-sensitive Kv current was smaller in 1K,1C-GBH rat than in normotensive rat. The voltage dependence of steady-state activation and inactivation of Kv channel determined by using double-pulse protocol showed no significant difference. These results suggest that 4-AP-sensitive Kv channels play a major role in the regulation of membrane potential in cerebral arterial smooth muscle cells and alterations of 4-AP-sensitive Kv channels would contribute to hypopolarization of membrane potential in 1K,1C-GBH rat.

Role of K+ channels to resting membrane potential of rabbit middle cerebral arterial smooth muscle cells

The aim of the present study is to investigate the contribution of Ca2+-activated K+ (KCa) channels and delayed rectifier K+ (KV) channels to the resting membrane potential (RMP) in rabbit middle cerebral arterial smooth muscle cells. The RMP and membrane currents were recorded using the whole-cell patch configuration and single KCa channel was recorded using the outside-out patch configuration. Using the pipette solution containing 0.05 mM EGTA, the RMP was -25.76+/-5.08 mV (n=12) and showed spontaneous transient hyperpolarizations (STHPs). The membrane currents showed time- and voltage-dependent outward currents with spontaneous transient outward currents (STOCs). When we recorded the membrane potential using the pipette solution containing 10 mM EGTA, the RMP was depolarized and did not show STHPs. The membrane currents showed no STOCs but only showed slowly inactivating outward currents. External TEA (1 mM) reversibly inhibited the STHPs, depolarized the RMP, reduced the membrane currents, abolished STOCs, and decreased the open probability of single KCa channel. When KV currents were isolated, the application of 4-AP (5 mM) depolarized the RMP. The important aspect of our results is that KCa channel is responsible for the generation of the STHPs in the membrane potential and plays an important role in the regulation of the RMP and KV channel is also responsible for the regulation of the RMP in rabbit middle cerebral arterial smooth muscle cells.