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  • Title: Dihydropyridine calcium agonists selectively enhance resistance artery myogenic tone.
    Author: Hwa JJ, Bevan JA.
    Journal: Eur J Pharmacol; 1986 Jul 31; 126(3):231-8. PubMed ID: 2428633.
    Abstract:
    Upon stretch in normal physiological salt solution (PSS), two dihydropyridine (DHP) Ca2+ agonists (Bay k 8644 and CGP 28392) enhanced the level of stretch-dependent myogenic tone in rabbit ear resistance arteries. This potentiating effect was not blocked by phenoxybenzamine (1 microM) and was Ca2+-dependent. Bay k 8644 was more potent than CGP 28392. These agonists had a smaller potentiating effect on K+ (20 mM)-induced contraction, and had little effect in the presence of high K+ (50-134 mM) PSS. Stretch-dependent myogenic tone is resistant to the inhibitory effect of nimodipine, a selective DHP Ca2+ antagonist which inhibited K+ (50 mM)-induced contraction in the nanomolar range. The potentiating effects of Bay k 8644 and CGP 28392 on myogenic tone were reversed by nimodipine. Our data suggest that DHP Ca2+ agonists selectively enhance myogenic tone by a mechanism that is antagonized by nimodipine, although physiological activation of myogenic tone is nimodipine insensitive, and the calcium related mechanisms of myogenic tone are distinct from those for high K+ depolarization-induced tone.
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