Browsing by Author "HERNANDEZ, D"

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    ELECTROPHYSIOLOGICAL CHARACTERISTICS OF CARDIAC-PACEMAKER CELLS OF THE FROG CAUDIVERBERA-CAUDIVERBERA
    (1987) HERNANDEZ, D; GUERRERO, S; MORALES, M
    The cardiac pacemaker cells of the frog Caudiverbera caudiverbera are centrally located in the sinus venosus. These cells are rounded, smaller than contractile fibres and have large nuclei. Intracellular recording confirmed the existence of primary and transitional pacemaker cells. Action potentials from primary cells were resistant to blockade by tetradotoxin (TTX), but were abolished by verapamil suggesting that their bioelectric activity is dependent on a slow inward current. Transitional cells appeared to have two different inward currents contributing to the upstroke: a fast TTX-sensitive and a slow verapamil-sensitive current.
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    ELECTROPHYSIOLOGICAL EFFECTS OF VERAPAMIL ON PRIMARY AND TRANSITIONAL PACEMAKER CELLS OF THE FROG-HEART
    (1988) MORALES, M; HERNANDEZ, D; DEGUEVARA, RL; GUERRERO, S
    In spontaneously beating preparations of sinus venosus of the frog Caudiverbera caudiverbera the electro-physiologic effects of verapamil on action potential parameters of both primary and transitional pacemaker cells were investigated. Verapamil in concentrations ranging from 5 .times. 10-8 M to 2 .times. 10-6 M slowed the sinus rate and blocked impulse initiation. Action potential blockade was accompanied by oscillations of membrane potential and depolarization. During blockade of primary pacemaker cells, pacemaker shift originated the activation of transitional or atrial contractile fibres. Subthreshold concentrations of the drug to induce complete blockade (5 .times. 10-8 M) allowed to observe a greater depression of bioelectric cell characteristics in primary than in transitional fibres. Verapamil-induced blockade of transitional pacemaker action potentials was preceded by the appearance of a notch in their upstroke and the persistence of a fast depolarizing section that remained unblocked. This fast verapamil-resistant section of the upstroke was absent in preparations treated with tetrodotoxin (TTX). The results confirmed most previously described actions of verapamil on mammalian sinoatrial preparations and provided a pharmacological dissection of the two slow and fast bio-electric components contributing to the upstroke of transitional pacemaker cells of the frog sinus venosus.