Sodium-Coupled Neutral Amino Acid Cotransporter Inhibited by the Volatile Anesthetic, Halothane, in Megakaryocytes.

Abstract

We have studied the effects of halothane, a popular volatile anesthetic, on Na(+)-coupled L-alanine cotransporters using rat bone marrow megakaryocytes subjected to patch-clamp whole-cell recordings. L-Alanine applied externally induced an immediate current response which was abolished by the elimination of external NaCl. The optical isomer, D-alanine, induced no such response. A ligand probe for the Na(+)-dependent amino-acid cotransporter (A-system), 2-methylaminoisobutyrate, induced a response comparable to that of L-alanine. The response was fitted by a Michaelis-Menten equation with a Km of 2.5 and 58.5 mM for L-alanine (with 120 mM Na+) and external Na+ (with 10 mM L-alanine), respectively. The volatile anesthetic, halothane, acutely and reversibly inhibited the inward current responsible for the Na(+)-coupled L-alanine cotransporter. Complete inhibition was attained at 1 mM, and 50%-inhibition at 0.35 mM. Halothane in a clinically relevant concentration reduced nutrient uptake via the cotransporter A-system. The sensitivity of the A-system to halothane is comparable to or greater than that of Na+/K+/Cl- cotransporter, sodium/proton exchange, stimulus-secretion coupling, and of many ion channels in nerve cells.

Compensatory Thrombopoietin Production from the Liver and Bone Marrow Stimulates Thrombopoiesis of Living Rat Megakaryocytes in Chronic Renal Failure

“…Single megakaryocytes were isolated from rat bone marrow as described in our previous studies [17, 18, 19]. Briefly, bone marrow obtained from femoral bones was flushed with standard external solution containing (in m M ): NaCl, 145; KCl, 4.0; CaCl 2 , 1.0; MgCl 2 , 2.0, and HEPES, 5.0 (pH 7.2 adjusted with NaOH), and disseminated by repetitive pipetting.…”

“…Single megakaryocytes were subjected to standard patch clamp whole-cell recording techniques, using an EPC-9 patch clamp amplifier system (Heka Electronics, Lambrecht, Germany), as described previously [17, 18, 19]. The patch pipette resistance was 1–3 MΩ when filled with internal (patch pipette) solution containing (in m M ): KCl, 145; MgCl 2 , 1.0; EGTA, 10, and HEPES, 5.0 (pH 7.2 adjusted with KOH).…”

Inhibition of Translation Initiation by Volatile Anesthetics Involves Nutrient-sensitive GCN-independent and -dependent Processes in Yeast

“…Such pathways may be activated in neuronal cells deprived of basal levels of neurotransmitter input, causing cells to suspend normal activity and enter a special state resulting in anesthesia. Given that 1) amino acids (e.g., glutamate, aspartate, and glycine) and their derivatives (e.g., GABA, serotonin, catecholamines, histamine, and nitric oxide) are neurotransmitters; 2) amino acids (e.g., leucine) play a key role in neurotransmitter metabolism (Yudkoff et al, 1994(Yudkoff et al, , 1997; and 3) volatile anesthetics affect transport of amino acids (Shimada et al, 1995) and neurotransmitters (Martin et al, 1990;elMaghrabi and Eckenhoff, 1993;Larsen and Langmoen, 1998;Sugimura et al, 2001) in mammals, these are reasonable possibilities. Transport of amino acids and their derivatives plays critical roles in transmitter synthesis and nerve transmission ( Figure 8B).…”