In vitro activity: Ketanserin causes a dose-dependent inhibition on the contractile responses to 5-hydroxytryptamine of isolated rat caudal artery, canine basilar, carotid, coronary and gastrosplenic arteries, canine gastrosplenic veins and canine saphenous veins. Ketanserin inhibits the contractions of rat caudal arteries and canine saphenous veins caused by postjunctional alpha adrenergic activation. Ketanserin depresses and in certain experiments reverses the vasoconstrictor response to 5-hydroxytryptamine in the perfused guinea-pig stomach. Ketanserin is found to attenuate the excitatory responses produced by norepinephrine, an alpha 1-adrenoceptor-mediated response, in the lateral geniculate nucleus. Ketanserin potentiates rather than attenuates, the inhibitory effect of 5-HT in the lateral geniculate nucleus. Ketanserin significantly prolongs action potential duration (APD) at 50% repolarization by 218% and APD at 90% repolarization by 256% with no significant effect on other action potential parameters in rat ventricular myocytes. Ketanserin results in a concentration- and time-dependent inhibition of charge area of Ito evaluated by integration with an EC50 of 8.3 μM. Ketanserin also blocks Ito and sustained current (ISus) in a dose-dependent manner with an EC50 of 11.2 μM and has no significant effect on both the inward rectifier potassium current and the L-type calcium current.

Cell Assay: The established HEK 293 cell line stably expressing hERG channels is cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% foetal bovine serum, 400 μg/mL G418. The HEK 293 cell line stably expressing recombinant human cardiac KCNQ1/KCNE1 channel current (IKs) is maintained in DMEM containing 10% foetal bovine serum and 100 μg/mL hygromycin. Cells used for electrophysiology are seeded on a glass coverslip. The mutant hERG channels are constructed, and are transiently expressed in HEK 293 cells using 10 μL of Lipofectamine 2000 with 4 μg of hERG mutant cDNA in pCDNA3 vector.