Circulation Research, Vol 67, 469-480, Copyright © 1990 by American Heart Association

ARTICLES

Actions of Ca2+ antagonists on two types of Ca2+ channels in rat aorta smooth muscle cells in primary culture

T Kuga, J Sadoshima, H Tomoike, H Kanaide, N Akaike and M Nakamura
Research Institute of Angiocardiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.

Mechanisms of blockade of two types of Ca2+ channels by the organic Ca2+ antagonists, nicardipine, diltiazem, verapamil, and flunarizine, were examined in rat aorta smooth muscle cells in primary culture by using the whole-cell voltage-clamp method. T-type Ca2+ current (T-type ICa) was isolated by an internal perfusion of 5 mM F-, which irreversibly suppressed the L-type ICa, without affecting T-type ICa. L- type ICa was isolated by setting a holding potential at -60 mV, at which most of the T-type Ca2+ channels were inactivated. L-type ICa is halved by 0.1 microM nicardipine, 3.0 microM diltiazem, 0.6 microM verapamil, and 0.1 microM flunarizine, whereas T-type ICa is halved by the same drugs at 0.6, 30, 30, and 0.1 microM, respectively. Diltiazem and verapamil accelerated the decay of L-type ICa and cumulatively blocked L-type ICa during repetitive step depolarizations elicited every 30 seconds ("use-dependent block"). Diltiazem and verapamil neither changed the decay of T-type ICa nor showed a use-dependent block of T-type ICa. Nicardipine and flunarizine blocked both L- and T- type ICa from the first depolarization step after drug treatment ("tonic block") and shifted their steady-state inactivation curves to the left. The estimated binding constants of nicardipine and flunarizine for the inactivated state of T-type Ca2+ channels (48 and 19 nM, respectively) were smaller than those for the resting state of L- type Ca2+ channels (160 and 90 nM, respectively). A low concentration (0.1 microM) of nicardipine initially potentiated T-type ICa and then reduced it. We conclude from these results that 1) nicardipine and flunarizine block not only the resting state but, more preferentially, the inactivated state of both the L- and T-type Ca2+ channels; 2) verapamil and diltiazem preferentially act on the open state of the L- type Ca2+ channel and on the resting and inactivated state of the T- type Ca2+ channel; and 3) the T-type Ca2+ channel of the rat aorta smooth muscle cells appears to be more sensitive to nicardipine and flunarizine than does the L-type Ca2+ channel at around the resting membrane potential.

This article has been cited by other articles:

				R. Fukunaga, K. Hirano, M. Hirano, N. Niiro, J. Nishimura, Y. Maehara, and H. Kanaide Upregulation of proteinase-activated receptors and hypercontractile responses precede development of arterial lesions after balloon injury Am J Physiol Heart Circ Physiol, November 1, 2006; 291(5): H2388 - H2395. [Abstract] [Full Text] [PDF]

				B. S. Freeze, M. M. McNulty, and D. A. Hanck State-Dependent Verapamil Block of the Cloned Human Cav3.1 T-Type Ca2+ Channel Mol. Pharmacol., August 1, 2006; 70(2): 718 - 726. [Abstract] [Full Text] [PDF]

				L. I. Brueggemann, B. L. Martin, J. Barakat, K. L. Byron, and L. L. Cribbs Low voltage-activated calcium channels in vascular smooth muscle: T-type channels and AVP-stimulated calcium spiking Am J Physiol Heart Circ Physiol, February 1, 2005; 288(2): H923 - H935. [Abstract] [Full Text] [PDF]

				E. Perez-Reyes Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels Physiol Rev, January 1, 2003; 83(1): 117 - 161. [Abstract] [Full Text] [PDF]

				L. A. Shimoda, J. S. K. Sham, T. H. Shimoda, and J. T. Sylvester L-type Ca2+ channels, resting [Ca2+]i, and ET-1-induced responses in chronically hypoxic pulmonary myocytes Am J Physiol Lung Cell Mol Physiol, November 1, 2000; 279(5): L884 - L894. [Abstract] [Full Text] [PDF]

				O. Vallot, L. Combettes, P. Jourdon, J. Inamo, I. Marty, M. Claret, and A.-M. Lompre Intracellular Ca2+ Handling in Vascular Smooth Muscle Cells Is Affected by Proliferation Arterioscler Thromb Vasc Biol, May 1, 2000; 20(5): 1225 - 1235. [Abstract] [Full Text] [PDF]

				S. Kataoka, R. Alam, P. K. Dash, and F. M. Yatsu Inhibition of PDGF-Mediated Proliferation of Vascular Smooth Muscle Cells by Calcium Antagonists Stroke, February 1, 1997; 28(2): 364 - 369. [Abstract] [Full Text]

				T. Kuga, S. Kobayashi, Y. Hirakawa, H. Kanaide, and A. Takeshita Cell Cycle-Dependent Expression of L- and T-Type Ca2+ Currents in Rat Aortic Smooth Muscle Cells in Primary Culture Circ. Res., July 1, 1996; 79(1): 14 - 19. [Abstract] [Full Text]

				S. N. Orlov, J. Tremblay, and P. Hamet cAMP Signaling Inhibits Dihydropyridine-Sensitive Ca2+ Influx in Vascular Smooth Muscle Cells Hypertension, March 1, 1996; 27(3): 774 - 780. [Abstract] [Full Text]