Alpha-adrenergic blockade with phentolamine reveals a strong dependence of frog sinus venosus pacemaker activity on extracellular calcium.
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Phentolamine unmasks Ca2+ dependence in frog pacemakers; hypothesis-generating for alpha-adrenergic effects on mammalian sinus node function.
The frog sinus venosus shows spontaneous regular pacemaker activity, even in the absence of extracellular Ca2+. When an alpha-adrenergic blocking agent (phentolamine) is applied, the rate of pacemaker activity, height of action potential, rate of slow diastolic depolarization, and the maximum diastolic potential become strongly dependent upon the extracellular Ca2+ concentration.
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Yasuichiro Fukuda (1986) studied this question.
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