Effect of mefloquine on the mechanical activity of the mouse isolated rectal smooth muscle.

The effects of mefloquine on the mechanical activity of the mouse isolated rectal smooth muscle was studied. Mefloquine (4.1 x 10(-5) - 5.2 x 10(-3)M) when applied alone and separately exerted variable effects on the rectum. In some preparations, it caused slight phasic contractions while in others no response was elicited. When the external Ca(2+) was increased from 1.8 mM to 300 mM mefloquine produced phasic contractile activity which was abolished on return to normal 1.8mM suggesting that the contractile activity was due to extracellular Ca(2+) influx. Mefloquine [4.1 x 10(-6)M - 4.1 x 10(-4)M] caused contraction-dependent inhibition of KCL, Carbachol and CaCl2 [in depolarizing Tyrode solution]. Mefloquine [2.1 x 10(-4)M] blocked KCL, but not carbachol contractions which were largely reversed by increasing [Ca2+]. The results show that mefloquine possesses anticholinergic and appreciable calcium channel blocking activity.