title: Dihydropyridine-insensitive calcium currents contribute to function of small cerebral arteries.
abstract: Although dihydropyridines are widely used for the treatment of vasospasm, their effectiveness is questionable, suggesting that other voltage-dependent calcium channels (VDCCs) contribute to control of cerebrovascular tone. This study therefore investigated the role of dihydropyridine-insensitive VDCCs in cerebrovascular function. Using quantitative PCR and immunohistochemistry, we found mRNA and protein for L-type (Ca(V)1.2) and T-type (Ca(V)3.1 and Ca(V)3.2) channels in adult rat basilar and middle cerebral arteries and their branches. Immunoelectron microscopy revealed both L- and T-type channels in smooth muscle cell (SMC) membranes. Using patch clamp electrophysiology, we found that a high-voltage-activated calcium current, showing T-type channel kinetics and insensitivity to nifedipine and nimodipine, comprised approximately 20% of current in SMCs of the main arteries and approximately 45% of current in SMCs from branches. Both components were abolished by the T-type antagonists mibefradil, NNC 55-0396, and efonidipine. Although nifedipine completely blocked vasoconstriction in pressurized basilar arteries, a nifedipine-insensitive constriction was found in branches and this increased in magnitude as vessel size decreased. We conclude that a heterogeneous population of VDCCs contributes to cerebrovascular function, with dihydropyridine-insensitive channels having a larger role in smaller vessels. Sensitivity of these currents to nonselective T-type channel antagonists suggests that these drugs may provide a more effective treatment for therapy-refractory cerebrovascular constriction.
authors.affiliation: John Curtin School of Medical Research, ANU College of Medicine, Biology and Environment, The Australian National University, Canberra, Australian Capital Territory, Australia.
authors.forename: Ivana Y
authors.initials: IY
authors.lastname: Kuo
authors.forename: Anthie
authors.initials: A
authors.lastname: Ellis
authors.forename: Victoria A L
authors.initials: VA
authors.lastname: Seymour
authors.forename: Shaun L
authors.initials: SL
authors.lastname: Sandow
authors.forename: Caryl E
authors.initials: CE
authors.lastname: Hill
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020747:Calcium Channels, T-Type / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002536:Cerebral Arteries / Q000378:metabolism* / Q000648:ultrastructure; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D004095:Dihydropyridines / Q000494:pharmacology*; D008297:Male; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D004095:Dihydropyridines; C038806:1,4-dihydropyridine; D002118:Calcium