PT  - JOURNAL ARTICLE
AU  - Wu, Songwei
AU  - Zhang, Min
AU  - Vest, Pamela A.
AU  - Bhattacharjee, Arin
AU  - Liu, Li
AU  - Li, Ming
TI  - A Mibefradil Metabolite Is a Potent Intracellular Blocker  of L-Type Ca<sup>2+</sup> Currents in Pancreatic β-Cells
DP  - 2000 Mar 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 939--943
VI  - 292
IP  - 3
4099  - http://jpet.aspetjournals.org/content/292/3/939.short
4100  - http://jpet.aspetjournals.org/content/292/3/939.full
SO  - J Pharmacol Exp Ther2000 Mar 01; 292
AB  - It has been shown that mibefradil (Ro 40-5967) exerts a selective inhibitory effect on T-type Ca2+ currents, although at higher concentrations it can antagonize high voltage-activated Ca2+ currents. The action of mibefradil on Ca2+channels is use- and steady-state-dependent and the binding site of mibefradil on L-type Ca2+ 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 Ca2+currents in insulin-secreting cells. However, the effect on L-type Ca2+ 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 Ca2+ current, whereas mibefradil exerted no effect. This study demonstrates that mibefradil permeates into cells and is hydrolyzed to a metabolite that blocks L-type Ca2+ channels specifically by acting at the inner side of the channel. The American Society for Pharmacology and Experimental Therapeutics