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1 Departments of Medical Physics and 2 Pharmacotherapy, Academic Medical Center, University of Amsterdam, 1100 DE Amsterdam, The Netherlands; and 3 Department of Physiology and Pharmacology, University of Southern Denmark-Odense University, DK-5000 Odense, Denmark
T-type calcium channels may be
involved in the maintenance of myogenic tone. We tested their role in
isolated rat cremaster arterioles obtained after CO2
anesthesia and decapitation. Total RNA was analyzed by RT-PCR and
Southern blotting for calcium channel expression. We observed
expression of voltage-operated calcium (CaV) channels
CaV3.1 (T-type), CaV3.2 (T-type), and
CaV1.2 (L-type) in cremaster arterioles (n = 3 rats). Amplification products were observed only in the presence of
reverse transcriptase and cDNA. Concentration-response curves of the
relatively specific L-type blocker verapamil and the relatively
specific T-type blockers mibefradil and nickel were made on cannulated
vessels with either myogenic tone (75 mmHg) or a similar level of
constriction induced by 30 mM K+ at 35 mmHg. Mibefradil and
nickel were, respectively, 162-fold and 300-fold more potent in
inhibiting myogenic tone compared with K+-induced
constriction [log(IC50, M): mibefradil, basal 
7.3 ± 0.2 (n = 9) and K+ 5.1 ± 0.1 (n = 5); nickel, basal 4.1 ± 0.2 (n = 5) and K+ 1.6 ± 0.5 (n = 5); means ± SE]. Verapamil had a 17-fold
more potent effect [log(IC50, M): basal 6.6 ± 0.1 (n = 5); K+ 5.4 ± 0.3 (n = 4); all log(IC50) P < 0.05, basal vs. K+]. These data suggest that T-type
calcium channels are expressed and involved in maintenance of myogenic
tone in rat cremaster muscle arterioles.
arteriole; CaV3.1; CaV3.2; mibefradil; nickel
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