The Effects of Ketamine on Ca2+ Movements in A7r5 Vascular Smooth Muscle Cells

Vasorelaxant mechanisms of ketamine in rabbit renal artery

Background

Ketamine is a non-barbiturate anesthetic agent which has various effects on the cardiovascular system. Among them, ketamine is known for its hypotensive properties. The hypotension is thought to be mediated by a direct effect on vascular smooth muscles. This study is designed to examine the effects of ketamine on KCl- and histamine-induced contraction in isolated rabbit renal arteries.

Methods

Endothelium-intact or -denuded smooth muscle rings were prepared and mounted in myographs for isometric tension measurements. The inhibitory effect of ketamine were investigated in smooth muscle rings precontracted with either 50 mM KCl- or 10 µM histamine.

Results

Ketamine (0.1-100 µg/ml) produced similar concentration-dependent inhibition of contractile responses induced by either 50 mM KCl or 10 µM histamine. The respective IC₅₀ values measured for ketamine following precontractions by 50 mM KCl and 10 µM histamine were 28.9 µg/ml (105.5 µM) and 26.7 µg/ml (97.5 µM). The inhibitory effect of 30 µg/ml ketamine were similarly observed after removal of endothelium or pretreatment with N^G-Nitroarginine Methyl Ester (0.1 mM). The inhibitory effect of 30 µg/ml ketamine on histamine-evoked contraction was reduced by either tetraethylammonium (10 mM) or iberiotoxin, a large conductance Ca²⁺-activated K⁺ channel blocker. However, depletion of intracellular Ca²⁺ stores by ryanodine (10 µM) or thapsigargin (10 µM) showed no significant effect on 30 µg/ml ketamine-induced relaxation. Pre-incubation with 30 µg/ml ketamine significantly inhibited CaCl₂-induced contraction at almost all ranges of concentration.

Conclusions

Ketamine-induced relaxation of rabbit renal arteries is mediated by both the activation of large conductance Ca²⁺-activated K⁺ channel and the inhibition of Ca²⁺ influx.

Stimulation of DNA synthesis, activation of mitogen-activated protein kinase ERK2 and nuclear accumulation of c-fos in human aortic smooth muscle cells by ketamine

Proliferation of vascular smooth muscle cells is known to be regulated by autocrine and paracrine stimuli, including extracellular matrix, reactive oxygen species, lipids, and biomechanical forces. The effect of many pharmacological agents to which smooth muscle cells may be exposed, however, is widely unexplored. Ketamine, an intravenous anaesthetic and a phencyclidine derivative, regulates diverse intracellular signalling pathways in smooth muscle cells, several of which are known to affect cell proliferation. The effect of ketamine on proliferative response of smooth muscle cells, however, is not determined. We tested the hypothesis that ketamine may regulate proliferation of smooth muscle cells, and investigated the effects of pharmacological doses of ketamine on their proliferative capacity by measuring DNA synthesis and activation of mitogen-activated protein (MAP) kinase signalling pathway in human aortic smooth muscle cells. DNA synthesis, as determined by incorporation of 3H-thymidine into DNA, was enhanced by 73% (P < 0.0001) and 130% (P < 0.0001) with 10 and 100 microm ketamine, respectively. Ketamine-induced DNA synthesis was dependent on de novo protein synthesis, as it was abolished by an inhibitor of protein synthesis, cycloheximide. A synthetic inhibitor of MAP kinase pathway, PD98059, decreased 50% (P < 0.0001) of ketamine-induced DNA synthesis, suggesting that the activation of MAP kinase pathway was partially responsible for ketamine-induced effects. Consistently, in-gel kinase assay and in vitro kinase assay of cell lysates showed ketamine-induced MAP kinase activation and expression of ERK2 (extracellular signal-regulated kinase) in smooth muscle cells. This effect of ketamine was not dependent on de novo protein synthesis. Immunofluorescent light microscopy showed ketamine-induced nuclear accumulation of c-fos, a downstream effect of MAP kinase activation, in smooth muscle cells. In conclusion, these data support the hypothesis of the study and demonstrate that ketamine, by stimulating DNA synthesis in human aortic smooth muscle cells, may have an impact on proliferative capacity of these cells. The present results also demonstrate that ketamine induces the activation of MAP kinase pathway and nuclear accumulation of transcription factor c-fos in smooth muscle cells. They further demonstrate that the activation of MAP kinases is partially responsible for ketamine-induced DNA synthesis in human aortic smooth muscle cells. Together, these findings suggest that ketamine may play a role as a pharmacological regulator of mechanisms involved in proliferation of smooth muscle cells.

Analysis of ketamine responses in the pulmonary vascular bed of the cat

OBJECTIVE

To test the hypothesis that pulmonary vasodilator responses of ketamine are dependent on activation of L-type calcium channels, independent of synthesis of nitric oxide from L-arginine, activation of adenosine triphosphate-sensitive potassium channels, and the release of cyclooxygenase products.

DESIGN

Prospective study.

SETTING

Research laboratory.

SUBJECTS

Isolated lobar lung preparation, mongrel cats.

INTERVENTIONS

In separate experiments, the effects of nicardipine; N omega-I-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase; glibenclamide, an adenosine triphosphate-sensitive potassium channel antagonist; and meclofenamate, a cyclooxygenase blocker, were investigated in the pulmonary vascular bed of the cat. The effects of these agents were evaluated on the pulmonary arterial responses of ketamine, acetylcholine, and isoproterenol during elevated tone conditions induced by the thromboxane A2 mimic, U46619 (Upjohn, Kalamazoo, MI).

MEASUREMENTS

Lobar arterial perfusion pressure, systemic pressure, and left atrial pressure were continuously monitored, electronically averaged, and permanently recorded.

MAIN RESULTS

Under elevated tone conditions in the isolated left lower lobe vascular bed of the cat, N omega-I-nitro-L-arginine methyl ester, glibenclamide, and meclofenamate had no significant effect on the vasodilator responses to ketamine. Nicardipine, in a dose that reduced significantly vasopressor effects to BAY K 8644, a calcium-channel opener, attenuated significantly vasodilator responses to ketamine, whereas the L-type calcium-channel blocker had no significant effects on responses to acetylcholine and to isoproterenol.

CONCLUSIONS

These data show that ketamine has significant vasodilator activity in the pulmonary vascular bed of the cat. The present data also suggest that responses to ketamine during elevated tone conditions may in part be mediated by the activation of L-type calcium channels.

Pulmonary vasodilation by ketamine is mediated in part by L-type calcium channels

We studied the effects of ketamine in the isolated rat lung under conditions of increased pulmonary arterial pressure using the thromboxane A2 mimic, U46619, and in response to ventilatory hypoxia. Ketamine caused dose-dependent vasodilation, and possible mechanisms were evaluated using verapamil, meclofenamate, N(omega)-L-nitro-L-arginine benzyl ester (an inhibitor of nitric oxide synthase), and U-38883A (an ATP-sensitive potassium channel antagonist) in the isolated blood-perfused rat lung. Under increased tone conditions, N(omega)-L-nitro-L-arginine benzyl ester, meclofenamate, and U-38883A had no significant effect in attenuating ketamine-induced vasodilator responses. In a final series of experiments, verapamil significantly attenuated ketamine-induced vasodilator responses. These data suggest that ketamine has significant vasodilator activity in the pulmonary vascular bed of the rat, which seems to be mediated by an L-type calcium channel-sensitive pathway. These responses are not mediated or modulated by the release of nitric oxide, the activation of K+ ATP channels, or the release of vasodilator cyclooxygenase products.

IMPLICATIONS

In this study, we examined the mechanism of the vasodilator effects of ketamine in the blood-perfused rat lung. The results of the present study suggest that ketamine-induced vasodilator responses are mediated by an L-type calcium channel-sensitive pathway.