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ABSTRACT Previous data from our laboratory suggest that the newborn (NB) rabbit heart is greatly dependent on extracellular calcium (Ca) for excitation-contraction coupling. Verapamil (V), a

calcium antagonist, is currently being used to treat arrhythmias in infaits. Little is known about the negative inotropic effects of this agent on NB hearts. This study was designed to

evaluate the effects of V on mechanical function of the neonatal heart. NB (n=6) and adult (A,n=6) rabbit hearts were studied utilizing an isolated, arterially perfused cardiac preparation

that was maintained at 27°C and paced at 36 beats/min. The muscles were perfused initially with a control Krebs-Henseleit solution (K-HS) and then with a K-HS containing 0.1 uM of V. Peak

(PT), developed (DT), resting (RT) tensions; rate of tension development (+dT/dt); time to peak tension (TPT); and time to half relaxation (1/2 RLT) were recorded continuously. The negative

inotropic effect of V in the NB was significantly (P<0.01) less than that in the A. In the NB, 50% of the maximal decrease in function occurred significantly (P=0.03) later than it did in

the A. V significantly (P<0.04) increased the RT in the NB but not in the A. V had no significant effect on either the TPT or the 1/2 RLT in the two age groups. These data suggest that

the negative inotropic effect of V in the NB is less than that in the A and that the NB is less dependent on the slow inward calcium current for excitation-contraction coupling than is the

A. ARTICLE PDF AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Pediatrics, UCLA Medical Center, Los Angeles Barbara L George, Toshio Nakanishl, Tatsuo Shimizu, Kenya Nishioka 

& Jay M Jarmakani Authors * Barbara L George View author publications You can also search for this author inPubMed Google Scholar * Toshio Nakanishl View author publications You can also

search for this author inPubMed Google Scholar * Tatsuo Shimizu View author publications You can also search for this author inPubMed Google Scholar * Kenya Nishioka View author

publications You can also search for this author inPubMed Google Scholar * Jay M Jarmakani View author publications You can also search for this author inPubMed Google Scholar RIGHTS AND

PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE George, B., Nakanishl, T., Shimizu, T. _et al._ 142 EFFECT OF VERAPAMIL ON MECHANICAL FUNCTION OF THE NEONATAL

RABBIT HEART. _Pediatr Res_ 15 (Suppl 4), 463 (1981). https://doi.org/10.1203/00006450-198104001-00151 Download citation * Issue Date: 01 April 1981 * DOI:

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