ISSN:
1432-1912
Keywords:
Phenylephrine
;
α-Adrenoceptor
;
Ca2+-dependent action potential
;
Rabbit papillary muscle
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Electrophysiological and mechanical effects of phenylephrine were observed in the rabbit papillary muscle which was depolarized and rendered inexcitable by an elevation of potassium concentration to 27 mM in the presence of a β-adrenoceptor blocking drug, bufetolol (10−6 M). 1. Phenylephrine (10−6 to 10−4 M) restored the action potential and tension development. The amplitude, duration and maximum rate of rise of the action potential, and developed tension were augmented by an increase in the concentration of phenylephrine. 2. The amplitude of the action potential restored by phenylephrine was very sensitive to the Ca2+ concentration and increased by 29.2 mV/10-fold increase crease in external Ca2+ concentration. Nifedipine (10−6 M), a Ca2+ antagonist, completely suppressed the electrical and mechanical responses restored by phenylephrine (10−5 M), but tetrodotoxin (10−5 M) had little effect on these responses. 3. Phentolamine (10−6 M) suppressed both the action potential and developed tension restored by phenylephrine (10−5 M), but the elevation of the concentration of bufetolol from 10−6 M to 3×10−6 M was ineffective against these responses. In conclusion, the restoration by phenylephrine of Ca2+-dependent action potential may be ascribed to an enhancement of the inward Ca2+ current, mediated by α-adrenoceptors and this mechanism may play an important role in the α-adrenoceptor-mediated positive inotropic effect.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00507038
Permalink
