Agents for the treatment of overactive detrusor. V. Synthesis and inhibitory activity on detrusor contraction of N-tert-butyl-4,4-diphenyl-2-cyclopentenylamine

Block and modified gating of cardiac calcium channel currents by terodiline

1. Terodiline, an anticholinergic/antispasmodic drug effective in the treatment of urinary incontinence, is presently restricted due to adverse side effects on cardiac function. To characterize its effects on cardiac L-type Ca2+-channel current carried by Ca2+ (ICa, L) and Ba2+ (IBa,L), concentrations ranging from 0.1 to 100 microM were applied to whole-cell-configured guinea-pig ventricular myocytes. 2. Although sub-micromolar concentrations of terodiline had no effect on ICa,L at 0 mV, 100 microM drug reduced its amplitude to ca. 10% of pre-drug control. The estimated IC50 (15.2 microM in K+-dialysed cells, 12.2 microM in Cs+-dialysed cells; 0.1 Hz pulsing rate) is eight times higher than reported for ICa,L in bladder smooth muscle myocytes. 3. Terodiline affected ICa,L in a use-dependent manner; block increased when the pulsing rate was increased from 0.1 to 2 - 3 Hz, and when holding potential was lowered from -43 mV. The drug accelerated the decay of ICa,L at 0 mV in a concentration-dependent manner, and slowed the recovery of channels from inactivation. 4. Terodiline reduced peak IBa,L more effectively than peak ICa,L, and markedly accelerated the rate of inactivation of the current. 5. The results are discussed in terms of mechanisms of Ca2+ channel block and relation to the therapeutic and cardiotoxic effects of the drug.

Inhibition of cardiac inward-rectifier K+ current by terodiline

The antispasmodic agent terodiline has cardiotoxic effects that include QT lengthening. To determine whether inhibition of inwardly-rectifying K+ current (I(K1)) might be a factor in the cardiotoxicity, we measured I(K1) in guinea pig ventricular myocytes. Terodiline reduced outward I(K1) with an IC50 of 7 microM; maximal reduction was 60% with 100-300 microM concentration. Inhibition was independent of current direction, and persisted after removal of the drug. Terodiline (3-5 microM) lengthened action potentials in guinea pig papillary muscles by ca. 10%, primarily by slowing phase 3 repolarization; higher concentrations abbreviated the plateau and markedly slowed late repolarization. Terodiline washout provoked an extra lengthening, consistent with persistent inhibition of I(K1) and rapid recovery of net inward plateau current. The results suggest that inhibition of I(K1) is a likely factor in the cardiotoxicity of the drug.