Characterization of sodium and pyruvate interactions of the two carrier systems specific of mono- and di- or tricarboxylic acids by renal brush-border membrane vesicles

Abstract

The experiments reported in this paper aim at characterizing the carboxylic acid transport, the interactions of pyruvate and citrate with their transport sites and specificity. The study of these carriers was performed using isotopic solutes for the influx measurements in brush-border membrane vesicles under zero trans conditions where the membrane potential was abolished with KCl preloading with valinomycin or equilibrium exchange conditions and delta psi = 0. Under zero trans condition and delta psi = 0, the influence of pyruvate concentrations on its initial rates of transport revealed the existence of two families of pyruvate transport sites, one with a high affinity for pyruvate (Kt = 88 microM) and a low affinity for sodium (Kt = 57.7 mM) (site I), the second one with a low affinity for pyruvate (Kt = 6.1 mM) and a high affinity for sodium (Kt = 23.9 mM) (site II). The coupling factor [Na]/[pyruvate] stoichiometry were determined at 0.25 mM and 8 mM pyruvate and estimated at 1.8 for site I, and 3 when the first and the second sites transport simultaneously. Under chemical equilibrium (delta psi congruent to 0) single isotopic labeling, transport kinetics of pyruvate carrier systems have shown a double interaction of pyruvate with the transporter; the sodium/pyruvate stoichiometry also expressed according to a Hill plot representation was n = 1.7. The direct method of measuring Na+/pyruvate stoichiometry from double labeling kinetics and isotopic exchange, for a time course, gives a n = 1.67. Studies of transport specificity, indicate that the absence of inhibition of lactate transport by citrate and the existence of competitive inhibition of lactate and citrate transports by pyruvate leads to the conclusion that the low pyruvate affinity site can be attributed to the citrate carrier (tricarboxylate) and the high pyruvate affinity site to the lactate carrier (monocarboxylate).

Zebrafish Slc5a12 Encodes an Electroneutral Sodium Monocarboxylate Transporter (SMCTn)

“…L-lactate ϭ 235 Ϯ 24 M and nicotinate ϭ 296 Ϯ 88 M (13,14,22,23). Taken together these data demonstrate that affinity of zSMCTn for L-lactate and nicotinate are ϳ10 times 7 and ϳ30 times lower than the affinity of zSMCTe for the same compounds, respectively (compare Fig. 4 with Fig.…”

“…Several studies have also reported the kinetics of renal Na ϩ /MC cotransport (7,8,12,34,40). These studies suggested the presence of two kinetically different Na ϩ /MC cotransport systems with one having higher affinity for MCs than the other.…”

“…Nicotinate Alters L-Lactate Transport by zSMCTn-Under normal physiological circumstances multiple monocarboxylates 7 The average unclamped voltages for zSMCTn oocytes (Fig. 4) for these experiments was Ϫ45 Ϯ 6 mV.…”

Transport of γ-Hydroxybutyrate in Rat Kidney Membrane Vesicles: Role of Monocarboxylate Transporters

“…The authors reported two sodium-driven electrogenic processes from whole cortex, pars convoluta, and pars recta, one of high affinity and the other of low affinity. Other reports in the literature have also confirmed the presence of a sodium-dependent transport process for L-lactate or pyruvate in mammalian kidney (BaracNieto et al, 1980;Nord et al, 1982;Mengual et al, 1989). Recently, the high-affinity sodium-dependent transport system for monocarboxylates has been identified as SLC5A8, a facilitated glucose transporter family member (Li et al, 2003;Miyauchi et al, 2004), and the low-affinity sodium-dependent transporter for monocarboxylates as SLC5A12 (Srinivas et al, 2005).…”

The Drug of Abuse γ-Hydroxybutyrate Is a Substrate for Sodium-Coupled Monocarboxylate Transporter (SMCT) 1 (SLC5A8): Characterization of SMCT-Mediated Uptake and Inhibition

“…In the kidney, SMCT1 is expressed in the apical membrane of tubular epithelial cells and is mainly limited to the S3 section of the proximal tubule. It was hypothesized that SMCT1 is involved in renal reabsorption of lactate and pyruvate (Gopal et al, 2007b;Ganapathy et al, 2008), because sodium-dependent transport of these monocarboxylates has been observed in the kidney (Barac-Nieto et al, 1980;Mengual et al, 1989). Moreover, SLC5A8-deficient or knockout mice exhibited increased urinary excretion of lactate (Frank et al, 2008).…”