Analysis of the potassium channel openers celikalim, pinacidil and cromakalim in platelet models of thrombosis

Ethnopharmacological studies on antispasmodic and antiplatelet activities of Ficus carica

ETHNOPHARMACOLOGICAL RELEVANCE

The ripe dried fruit of Ficus carica Linn. (Moraceae) commonly known as "Fig" has medicinal value in traditional system of medicine for its use in gastrointestinal and inflammatory disorders.

AIM OF THE STUDY

To rationalize the medicinal use of Fig (Ficus carica) in gastrointestinal and inflammatory disorders.

MATERIALS AND METHODS

The aqueous-ethanolic extract of Ficus carica (Fc.Cr) was studied for antispasmodic effect on the isolated rabbit jejunum preparations and for antiplatelet effect using ex vivo model of human platelets.

RESULTS

Fc.Cr tested positive for alkaloids, flavonoids, coumarins, saponins, sterols and terpenes. When tested in isolated rabbit jejunum, Fc.Cr (0.1-3.0mg/mL) produced relaxation of spontaneous and low K(+) (25 mM)-induced contractions with negligible effect on high K(+) (80 mM) similar to that caused by cromakalim. Pretreatment of the tissue with glibenclamide caused rightward shift in the curves of low K(+)-induced contractions. Similarly, cromakalim inhibited the contractions induced by low K(+), but not of high K(+), while verapamil equally inhibited the contractions of K(+) at both concentrations. Fc.Cr (0.6 and 0.12 mg/mL) inhibited the adenosine 5'-diphosphate and adrenaline-induced human platelet aggregation.

CONCLUSION

This study showed the presence of spasmolytic activity in the ripe dried fruit of Ficus carica possibly mediated through the activation of K(+)(ATP) channels along with antiplatelet activity which provides sound pharmacological basis for its medicinal use in the gut motility and inflammatory disorders.

Mechanisms of ischemic preconditioning in skeletal muscle

BACKGROUND

Ischemic preconditioning (IP) (one or more cycles each consisting of a short period of ischemia and a short period of reperfusion, before the sustained ischemia) reduces ischemia-related organ damage in heart and skeletal muscle but the underlying mechanisms are not clear. This study was intended to assess the possible involvement of K(ATP) channels and of adenosine receptors in IP of skeletal muscle in a rat model of skeletal muscle ischemia.

MATERIALS AND METHODS

Groups of 8-15 rats were given the following in vivo treatments: ischemia-reperfusion (I-R: 2.5 h tourniquet-induced ischemia of the right hindlimb, then 2 h reperfusion); IP (three cycles of 5 min ischemia, then 5 min reperfusion) before I-R; cromakalim and I-R; glibenclamide, cromakalim, and I-R; glibenclamide, IP, and I-R; [R]-N(6)-[1-methyl-2-phenylethyl]adenosine (R-PIA) and I-R; adenosine and I-R; and glibenclamide, IP, and I-R. Parameters of muscle function (postischemic maximal force, performance, contraction index, and force after 1 min of stimulation) were then assessed in vitro in the extensor digitorum longus muscle.

RESULTS

Pretreatment with either IP or the K(ATP) channel opener cromakalim significantly improved postischemic muscle function. The protective effect of cromakalim was not seen when the K(ATP) channel blocker glibenclamide was added. Glibenclamide, however, did not block IP-induced protection. Pretreatment with the adenosine A(1) receptor agonist 8-(p-sulfophenyl)-theophyllin (8-SPT) or with adenosine did not improve postischemic muscle function. The adenosine receptor agonist did not block IP-induced protection against ischemic damage.

CONCLUSIONS

The results show significant improvements in postischemic skeletal muscle function after IP or cromakalim pretreatment but they do not support a role for K(ATP) channels or for adenosine receptors in IP of skeletal muscle.

Potassium channel activation: a potential therapeutic approach?

The physiological role of K+ channel opening by endogenous substances (e.g., neurotransmitters and hormones) is a recognised inhibitory mechanism. Thus, the identification of novel synthetic molecules that 'directly' open K+ channels has led to a new direction in the pharmacology of ion channels. The existence of many different subtypes of K+ channels has been an impetus in the search for new molecules demonstrating channel and, thus, tissue selectivity. This review focuses on the different classes of openers of K+ channels, the intracellular mechanisms involved in the execution of their effects, and potential therapeutic targets.