Tonic Block of the Sodium and Calcium Currents by Ketamine in Isolated Guinea Pig Ventricular Myocytes.

Abstract

ABSTRACT. Effects of ketamine on the sodium (I Na ) and L-type calcium currents (I Ca ) were examined by using whole-cell patch clamp techniques in guinea pig single ventricular myocytes. The mode of action of ketamine was compared with those of quinidine, a sodium channel blocker, and verapamil, a calcium channel blocker. Ketamine (30-300 µM) inhibited both I Na and I Ca in a concentrationdependent manner. Quinidine (30 µM) and verapamil (0.1 µM) produced use-dependent depression of I Na and I Ca , respectively. The amplitude of I Na elicited by the first depolarizing pulse after a long quiescent period was slightly decreased by quinidine. During a train of depolarizing pulse the current amplitude decreased gradually, and reached a steady state level in the quinidine-treated cells (use-dependent block, UDB). Verapamil produced a similar mode of inhibition of I Ca , i.e., UDB. In contrast, ketamine produced significant decrease in I Na and I Ca elicited by the first depolarizing pulses and the decreases of both currents were not augmented during a train of depolarizing pulses. From these results, it can be concluded that ketamine produces tonic block of the cardiac sodium and calcium channels and the mode of inhibition is clearly different from UDB by quinidine and verapamil. -KEY WORDS: calcium current, cardiac myocyte, ketamine, sodium current, tonic block.J. Vet. Med. Sci. 60(4): 479-483, 1998 MATERIALS AND METHODSCell preparations: Guinea pigs, weighing 200-350 g, were used in this study. Single ventricular cells were isolated by an enzymatic dispersion, as previously described [11]. Briefly, the heart was removed from the open-chest guinea pig anesthetized with pentobarbital Na, and mounted on a modified Langendorff perfusion system for retrograde perfusion of the coronary circulation with a normal HEPESTyrode solution. The perfusion medium was then changed to a nominally Ca-free HEPES-Tyrode solution and then to a solution containing 0.02% w/v collagenase (Wako, Osaka, Japan). After digestion, the heart was perfused with a high K + and low Cl -solution (modified Kraftbrühe (KB) solution) [17,22]. Ventricular tissue was cut into small pieces in the modified KB solution and gently shaken to isolate cells. Dispersed cells were stored in the KB solution at 4°C and used over the next 7-10 hr.Recording techniques: Whole-cell membrane currents were recorded by patch clamp method [9]. Single ventricular cells were placed in a recording chamber (1-ml volume) attached to an inverted microscope (Olympus IMT-2, Tokyo, Japan) and superfused with the HEPES-Tyrode solution at a rate of 3 ml/min. The temperature of the external solution was kept constant at 36 ± 1°C. Glass patch pipettes with a diameter of 1.5 mm were filled with a pipette solution. The resistance of the patch pipette filled with the pipette solution was 2-3 MΩ. The tight-seal, whole cell voltage clamp technique was used. After the gigaohmseal between the tip of the electrode and the cell membrane was established, the membrane patch was disrupted by K...

Ketamine attenuates the Na+-dependent Ca2+ overload in rabbit ventricular myocytes in vitro by inhibiting late Na+ and L-type Ca2+ currents

“…i transients. Previous studies show that ketamine inhibits I CaL in the cardiomyocytes of some species [29][30][31][32][33][34] . However, no studies have investigated the effect of ketamine on I CaL in rabbit ventricular myocytes.…”

“…Hara et al reported that ketamine (30, 100, 300 μmol/L) dose-dependently blocked peak I Na in guinea pig ventricular myocytes [32] . However, no studies have investigated the effects of ketamine on I NaL in cardiomyocytes until now.…”

“…Ketamine has been reported to inhibit various ionic currents [29][30][31][32][33][34][35][36][37][38] . Hara et al reported that ketamine (30, 100, 300 μmol/L) dose-dependently blocked peak I Na in guinea pig ventricular myocytes [32] .…”

“…This result shows that there are additional mechanisms other than inhibiting I NaL underlying ketamine's suppressive effects. Previous studies show npg that ketamine inhibits I CaL in guinea pig and rat ventricular myocytes, in human right atrial myocytes and bullfrog atrial myocytes [29][30][31][32][33][34] . Hara et al reported that ketamine (30 μmol/L) decreased I CaL by 26.1% in guinea pig ventricular myocytes [32] .…”

“…These results suggest that ketamine may have cardioprotective effects, but the underlying mechanisms are still unknown. Ketamine has been reported to inhibit various ionic currents, including the L-type Ca 2+ current (I CaL ) [29][30][31][32][33][34] , peak sodium current (I Na ) [32] , inward rectifier K + current (I K1 ) [30,35] , delayed rectifier K + current (I K ) [30] , ATP-sensitive K + current (I KATP ) [36,37] , and human ether-a-go-go-related gene (hERG) channel [38] . However, there is no study regarding the effects of ketamine on I NaL .…”