title: The effect of [Ca]o on the resting potential in newborn and adult rat ventricular muscles.
abstract: Microelectrode studies were carried out to examine the effect of varied [Ca]o on resting potentials of newborn and adult rat ventricular muscles. The ratio of membrane permeabilities to sodium and potassium (PNa/PK) estimated from the constant-field equation was about 0.03 in 2 mM [Ca]o in both newborn and adult preparations. Membrane hyperpolarization was observed in adult preparations when [Ca]o was increased from 1 mM to 10 mM, whereas the resting potential of newborn preparations was little hyperpolarized. In 10 mM [Ca]o, PNa/PK was 0.01 in adult and was still 0.03 in newborn. The hyperpolarization observed in adult tissue was reduced in low [Na]o, which is inconsistent with the constant-field equation. A possible mechanism of this hyperpolarization is discussed.
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006352:Heart Ventricles; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002118:Calcium