| 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. |
