No abstract

In a study in 75 volunteers, preparations of interferon-beta1b (IFN-beta1b) and IFN-beta1a were compared in terms of the resulting serum concentrations of three biologic markers, neopterin, human Mx protein, and 2',5' oligoadenylate synthetase. Each preparation was tested at five dose levels, the middle dose being that recommended for use in patients with multiple sclerosis on the basis of large clinical trials. Five randomly chosen volunteers each received a single subcutaneous dose of one of the IFN or of IFN-beta1a given intramuscularly. The amounts of each marker induced were dose related. There were no major differences between the results with the two IFN or in the duration of the changes in the markers after the two routes of injection. The data indicated that 8 million international units (MIU) of IFN-beta1b and 6 MIU of IFN-beta1a had very similar effects. Even after the highest single dose tested, the increase in the biologic markers were not sustained for a full week.

A study has been made of electrogenic cellular uptake of amino acids resulting in the depolarization of cell membrane potential (PDm) in confluent monolayers of an established opossum kidney (OK) cell line using conventional and pH-selective microelectrodes. Apical superfusion of neutral and dibasic amino acids rapidly depolarized the cell membrane, while application of acidic amino acids had no effect on PDm. The depolarization in response to L-phenylalanine and L-arginine was stereoselective, dose-dependent and saturable. 10 mmol/l of L-phenylalanine reduced PDm by 4.8 +/- 0.4 mV (n = 51) in a completely sodium-dependent way and the concentration necessary for half-maximal depolarization (C1/2) was about 1.5 mmol/l. On the other hand, the C1/2 for L-arginine was about 0.02 mmol/l. The maximal depolarization produced by L-arginine (measured at 10 mmol/l) amounted to 6.8 +/- 1.2 mV (n = 10) and this was not affected when extracellular sodium was replaced by choline (6.3 +/- 1.2 mV; n = 10). The depolarizations induced by L-phenylalanine and L-arginine were significantly additive (p less than 0.001). The intracellular pH of OK cells was 7.09 +/- 0.03 (n = 11) and did not change during L-arginine application. We conclude that (1) carrier-mediated uptake of neutral and dibasic amino acids into OK cells is at least partially electrogenic. (2) L-Phenylalanine is transported by a Na+-symport. (3) In contrast, L-arginine depolarizes PDm independently of extracellular sodium. (4) Electrogenic uptake of acidic amino acids is not detectable in OK cells.

Confluent monolayers of the established opossum kidney cell line were exposed to NH4Cl pulses (20 mmol/liter) during continuous intracellular measurements of pH, membrane potential (PDm) and membrane resistance (R'm) in bicarbonate-free Ringer. The removal of extracellular NH4Cl leads to an intracellular acidification from a control value of 7.33 +/- 0.08 to 6.47 +/- 0.03 (n = 7). This inhibits the absolute K conductance (gK+), reflected by a decrease of K+ transference number from 71 +/- 3% (n = 28) to 26 +/- 6% (n = 5), a 2.6 +/- 0.2-fold rise of R'm, and a depolarization by 24.2 +/- 1.5 mV (n = 52). In contrast, intracellular acidification during a block of gK+ by 3 mmol/liter BaCl2 enhances the total membrane conductance, being shown by R'm decrease to 68 +/- 7% of control and cell membrane depolarization by 9.8 +/- 2.8 mV (n = 17). Conversely, intracellular alkalinization under barium elevates R'm and hyperpolarizes PDm. The replacement of extracellular sodium by choline in the presence of BaCl2 significantly hyperpolarizes PDm and increases R'm, indicating the presence of a sodium conductance. This conductance is not inhibited by 10(-4) mol/liter amiloride (n = 7). Patch-clamp studies at the apical membrane (excised inside-out configuration) revealed two Na(+)-conductive channels with 18.8 +/- 1.4 pS (n = 10) and 146 pS single-channel conductance. Both channels are inwardly rectifying and highly selective towards Cl-. The low-conductive channel is 4.8 times more permeable for Na+ than for K+. Its open probability rises at depolarizing potentials and is dependent on the pH of the membrane inside (higher at pH 6.5 than at pH 7.8).

1. The membrane potential of OK cells is largely determined by a pH-sensitive, barium-blockable K+-conductance. 2. Amiloride-blockable Na+/H+-exchange is reflected by membrane potential changes via this K+-conductance. 3. Monolayers of OK cells are electrically leaky.