Ionic Fluxes in the Rat Portal Vein and the Applicability of the Goldman Equation in Predicting the Membrane Potential from Flux Data

Abstract

Wahlstrom, B. A. Ionic fluxes in the rat portal vein and the applicability of the Goldman equation in predicting the membrane potential from flux data. Acta physiol. scand. 1973. 89. 436–448. The sodium, potassium and chloride effluxes from the rat portal vein were measured using radioactive tracer ions. It was found that the sodium efflux attributable to an intracellular compartment was very slow, with a rate constant of 4.66×10‐4 s‐1, and the corresponding intracellular sodium only 3.0 mmol/kg wetweight. The intracellular potassium exchanged with a rate constant of 2.15×10‐4 s‐1 and contained 45.5 mmol/kg wetweight. The intracellular chloride content was 14.7 mmol/kg wetweight, exchanging with a rate constant of 10.55 × 10‐4 s‐1. From these data the permeabilities of Na, K and CI were calculated to 0.130, 3.81 and 3.11 ×10‐8 cms‐1 respectively. The relative permeabilities PK: PNa: PC1 were 1: 0.034: 0.816, and from these values the Goldman equation predicted a membrane potential of ‐42.3 mV. The actual membrane potential, measured by glass microelectrodes, was ‐ 45 mV. It was concluded that the membrane potential in the rat portal vein in normal solution can be predicted from the permeabilities and distribution of K and CI, while Na plays an insignificant part.

Effect of the K+ efflux stimulating vasodilator BRL 34915 on 86Rb+ efflux and spontaneous activity in guinea‐pig portal vein

“…In the presence of PN 200-110,60 nM BRL 34915 augmented k by 4 ± I% (Table 1) which converts to an increase in potassium permeability of ,1.5 x 109cm s-'. Using the Goldman equation a resulting hyperpolarization of the membrane of -0.7mV was calculated (Wahlstrom (1973), parameters for rat portal vein). This crude estimate shows that, in principle, the 86Rb+ efflux method is of adequate sensitivity.…”

Ion Transport in Tonic and Phasic Vascular Smooth Muscle and Changes during Deoxycorticosterone Hypertension

“…The ionic basis for these differences is poorly understood. A comparison of isotope exchange in portal mesenteric vein [17] and aorta from rats [12] does not yield a consistent trend. The turnover of 42K was greater in the portal mesenteric vein whereas that for 24Na and 36C1 was less.…”

“…This has led to a classification of vas cular smooth muscle into phasic or tonic types [15]. One of the distin guishing features is that the portal mesenteric vein maintains a resting membrane potential which is less electronegative than the tonic type in rabbit [16] and rat [8,17]. The ionic basis for these differences is poorly understood.…”

Electrical responses of the smooth muscle of the guinea-pig cerebral artery to brief electrical stimulation.

“…In the rat portal vein, the equilibrium potentials of Na and Cl are positive while that of K is negative in respect to the resting membrane potential (WAHLSTROM, 1973). If this is applicable to the guinea-pig's cerebral artery, an increase of Na or Cl conductance of the membrane and a decrease of K conductance would depolarize the membrane.…”