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Articles in PresS, published online ahead of print September 5, 2002
Am J Physiol Heart Circ Physiol, 10.1152/ajpheart.00531.2002
Submitted on June 28, 2002
Accepted on August 26, 2002
1 Medical Physics, University of Amsterdam Academic Medical Center, Amsterdam, The Netherlands
2 Physiology and Pharmacology, University of Southern Denmark-Odense University, Odense, Denmark
3 Pharmacotherapy, University of Amsterdam Academic Medical Center, Amsterdam, The Netherlands
* To whom correspondence should be addressed. E-mail: e.vanbavel{at}amc.uva.nl.
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 Ca-channel expression. We observed expression of Cav3.1, Cav3.2 (T-types) 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 162x and 300x more potent in inhibiting myogenic tone as compared to potassium-induced constriction: log(IC50,M) Mibefradil: basal: -7.3±0.2 (SEM,n=9); K+: -5.1±0.1 (n=5); Nickel: basal: -4.1±0.2 (n=5), K+ -1.6±0.5 (n=5). Verapamil had a 17x more potent effect: log(IC50,M) basal: -6.6±0.1 (n=5); K+ -5.4±0.3 (n=4) (all log IC50's 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.
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