title: A mibefradil metabolite is a potent intracellular blocker of L-type Ca(2+) currents in pancreatic beta-cells.
abstract: It has been shown that mibefradil (Ro 40-5967) exerts a selective inhibitory effect on T-type Ca(2+) currents, although at higher concentrations it can antagonize high voltage-activated Ca(2+) currents. The action of mibefradil on Ca(2+) channels is use- and steady-state-dependent and the binding site of mibefradil on L-type Ca(2+) channels is different from that of dihydropyridines. By using conventional whole-cell and perforated patch-clamp techniques, we showed that mibefradil has an inhibitory effect on both T- and L-type Ca(2+) currents in insulin-secreting cells. However, the effect on L-type Ca(2+) currents was time-dependent and poorly reversible in perforated patch-clamp experiments. By using mass spectrometry, we demonstrated that mibefradil accumulates inside cells, and furthermore, a metabolite of mibefradil was detected. Intracellular application of this metabolite selectively blocked the L-type Ca(2+) current, whereas mibefradil exerted no effect. This study demonstrates that mibefradil permeates into cells and is hydrolyzed to a metabolite that blocks L-type Ca(2+) channels specifically by acting at the inner side of the channel.
authors.affiliation: Department of Pharmacology, University of South Alabama, College of Medicine, Mobile, Alabama, USA.
authors.forename: S
authors.initials: S
authors.lastname: Wu
authors.forename: M
authors.initials: M
authors.lastname: Zhang
authors.forename: P A
authors.initials: PA
authors.lastname: Vest
authors.forename: A
authors.initials: A
authors.lastname: Bhattacharjee
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Li
mesh_terms: D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D020747:Calcium Channels, T-Type / Q000187:drug effects; D002460:Cell Line; D007515:Islets of Langerhans / Q000187:drug effects*; D020748:Mibefradil / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D020748:Mibefradil