Effects of enflurane on the voltage-gated membrane currents of bovine adrenal chromaffin cells

Regulatory Effect of General Anesthetics on Activity of Potassium Channels

General anesthesia is an unconscious state induced by anesthetics for surgery. The molecular targets and cellular mechanisms of general anesthetics in the mammalian nervous system have been investigated during past decades. In recent years, K⁺ channels have been identified as important targets of both volatile and intravenous anesthetics. This review covers achievements that have been made both on the regulatory effect of general anesthetics on the activity of K⁺ channels and their underlying mechanisms. Advances in research on the modulation of K⁺ channels by general anesthetics are summarized and categorized according to four large K⁺ channel families based on their amino-acid sequence homology. In addition, research achievements on the roles of K⁺ channels in general anesthesia in vivo, especially with regard to studies using mice with K⁺ channel knockout, are particularly emphasized.

Is anesthesia caused by potentiation of synaptic or intrinsic inhibition? Recent insights into the mechanisms of volatile anesthetics

Volatile anesthetics modulate synaptic (GABAA receptor-mediated) and intrinsic (K+ channel-controlled) neuronal inhibition. GABAA receptor activity is enhanced, leading to increased charge transfer and prolonged synaptic inhibition, and members of the two pore domain family of potassium channels are activated, leading to neuronal hyperpolarization and reduced excitability. These effects may underlie different components of the complex anesthetic state.

Ketamine inhibition of large conductance Ca(2+)-activated K+ channels is modulated by intracellular Ca2+

The present investigation was conducted to study the relationship between intracellular Ca2+ and inhibition of large conductance Ca(2+)-activated K+ (BK) currents by ketamine using excised patches from GH3 cells. Five ketamine concentrations were studied in the presence of six Ca2+ concentrations. The half-maximal inhibition for BK channel block by ketamine was increased from 4.1 +/- 0.7 microM at 0.1 microM intracellular Ca2+ to 230 +/- 74 microM at 100 microM intracellular Ca2+. Open probability (Po), Ca2+ concentration, and ketamine concentration data were best described by a competitive inhibition model. The inhibition constant for ketamine was 20.5 +/- 5.2 microM, and the Michaelis-Menten constant (Km) value for Ca2+ was 3.58 +/- 0.49 microM, which was not different from Km for Ca2+ in the absence of ketamine (3.33 +/- 0.37 microM). Taken alone, these data would suggest that Ca2+ and ketamine were competing for the same site on the channel protein. However, examination of open and closed interval data from patches containing only one channel show that ketamine primarily produces a decrease in the frequency of long-lived open events, suggesting that the effect of ketamine on BK channels may not be by a direct effect on channel proteins.

The effect of racemic ketamine on the large conductance Ca(+2)-activated potassium (BK) channels in GH3 cells

Recently, inhalation anesthetics have been reported to block BK channels in adrenal chromaffin cells. To determine if BK block was characteristic only of inhalation anesthetics or was also a property of other general anesthetics we examined the effects of ketamine, an intravenous general anesthetic which is structurally different than inhalation anesthetics. Cell-attached and excised patch single channel and standard whole cell recording techniques were used to examine the effect of racemic ketamine on the BK channel activity in GH3 cells. When solutions containing 150 mM KCl are used in both the pipette and bath, the BK channels are characterized as a voltage-dependent channel with a unit conductance of 150-300 pS. Racemic ketamine (at clinically relevant concentrations; 2-500 microM) selectively blocked BK channels in a dose-dependent, reversible manner as evidenced by decreases in NPo (number of channels x open probability). This decrease was due to both a decrease in mean open time and an increase in the mean closed time but without a decrease in single-channel current amplitude. Ketamine shifts the Po vs voltage curve to higher potentials without a change in the slope of the voltage dependence. Ketamine also shifts the Po vs [Ca+2] relationship to higher Ca+2 concentrations. The IC50 for the single-channel block by ketamine is 20.3 +/- 15.9 microM. In an effort to confirm that the effect of ketamine was predominantly due to a block of the BK channels, standard whole cell techniques were utilized.(ABSTRACT TRUNCATED AT 250 WORDS)