Abstract 11277: Molecular Identification of a Nifedipine-Insensitive High Voltage-Activated Calcium Channel Widely Distributed in Mesenteric Arterioles
Introduction: Voltage-dependent calcium channels (VDCC) play important roles in vascular tone regulation, and it is generally believed that nifedipine-sensitive calcium channels (α1C) are the most important component in the control of blood pressure. However, we previously found and characterized a nifedipine-insensitive high voltage-activated calcium channel (NI-CC) which was widely distributed in guinea-pig, rabbit and rat arteriolar mesenteric smooth muscle and we showed that this channel also contributes to the regulation of blood flow (Circ Res. 1999; 85:596–605, etc). However, the molecular structure of NI-CC has not yet been identified. Taking account of previous reports (J Neurosci. 2001; 21:5944–51, J Neurosci. 2003; 23:6041–9), it appears that the hertero-multimeric α1D/β3/α2-δ1 channel shows similar electrophysiological and pharmacological properties of NI-CC.
Hypothesis: A novel type of calcium channel (α1D) in smooth muscle cells with accessory subunits (β3 and α2-δ1), could be the molecular entity of NI-CC.
Methods: VDCC current was recorded with patch-clamp from rat mesenteric artery myocytes or HEK293 cells which expressed α1D, β3, α2-δ1 cDNAs heterogously. RT-PCR, Western blot and immunofluorescent analyses were also employed for detecting the messenger RNAs and proteins in the arterial smooth muscle.
Results: Whole cell patch clamp technique revealed that electrophysiological properties (activation and inactivation kinetics, current-voltage relationship) of NI-CC and α1D/β3/α2-δ1 currents were nearly identical. Pharmacologically, α1D/β3/α2-δ1 was partially inhibited (30% of the control value) by nifedipine (10μM), but the rest of the current showed similar electrophysiological properties to NI-CC. Interestingly, both α1D/β3/α2-δ1 and NI-CC were completely inhibited by mibefradil (10μM), a potent T-type calcium channel blocker. RT-PCR, Western blot and immunostaining analyses showed α1D, β3 and α2-δ1 expression and their co-localization in plasma membrane of rat mesenteric arterial myocytes.
Conclusions: These results indicate that α1D/β3/α2-δ1 channel is the possible candidate for NI-CC which plays an important role in blood pressure regulation via controlling arteriolar circulation.
- © 2010 by American Heart Association, Inc.