A mibefradil metabolite is a potent intracellular blocker of L-type Ca(2+) currents in pancreatic beta-cells.
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.
Wu
S
S
Department of Pharmacology, University of South Alabama, College of Medicine, Mobile, Alabama, USA.
Zhang
M
M
Vest
P A
PA
Bhattacharjee
A
A
Liu
L
L
Li
M
M
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*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D020748:Mibefradil