Fused cells of frog proximal tubule: II. Voltage-dependent intracellular pH

Experiments were performed in intact proximal tubules of the doubly perfused kidney and in fused proximal tubule cells of Rana esculenta to evaluate the dependence of intracellular pH (pHi) on cell membrane potential applying pH-sensitive and conventional microelectrodes. In proximal tubules an increase of the K+ concentration in the peritubular perfusate from 3 to 15 mmol/liter decreased the peritubular cell membrane potential from -55 +/- 2 to -38 +/- 1 mV paralleled by an increase of pHi from 7.54 +/- 0.02 to 7.66 +/- 0.02. The stilbene derivative DIDS hyperpolarized the cell membrane potential from -57 +/- 2 to -71 +/- 4 mV and led to a significant increase of the K+-induced cell membrane depolarization, but prevented the K+-induced intracellular alkalinization. Fused proximal tubule cells were impaled by three microelectrodes simultaneously and cell voltage was clamped stepwise while pHi changes were monitored. Cell membrane hyperpolarization acidified the cell cytoplasm in a linear relationship. This voltage-induced intracellular acidification was reduced to about one-third when HCO-3 ions were omitted from the extracellular medium. We conclude that in proximal tubule cells pHi depends on cell voltage due to the rheogenicity of the HCO-3 transport system.

[In vitro studies of the cell cycle of mouse myelomonocytic leukemia using a fluorescence activated cell sorter and autoradiography]

Cell cycle and various phase time of mouse myelomonocytic leukemia cells were studied in vitro with Fluorescence Activated Cell Sorter (FACS 420, Becton-Dikinson FACS Systems, Sunnyvale, CA, USA) in testing cellular DNA content and with autoradiography. At the same time, doubling time was calculated by counting the number of cells cultured in vitro within 6 days following implantation. According to the cellular DNA content, the proportions of various cell phases in the whole cell population were as follows: G1, S and G2 plus M phases take up 30.5%, 47.9% and 21.6%. Basing on autoradiography and direct counting, the cell number, the cell cycle, duration of various cell phases and doubling time were as follows: LI = 98.0%, MI = 1.7 +/- 0.9%, TG1 = 4.9 hrs, TS = 8.0 hrs, TG2 = 2.8 hrs, Tm = 0.3 hr, TC = 16.0 hrs, TD = 17.0 hrs. FACS assay showed that the duration of various cell phases are quite similar to that calculated by autoradiography. Therefore a simple and rapid FACS method may be widely used in the studies of cell cycle instead of autoradiography if estimating computer program is available.

Antagonism by propranolol of the inhibitory effect of phenoxybenzamine on noradrenaline uptake in vivo

The reduction of noradrenaline stores and [3H]noradrenaline concentration in the heart of mice and rats induced by phenoxybenzamine-treatment, alone or in combination with cold-stress, was prevented by propranolol. Propranolol also antagonized a similar effect induced by phentolamine but not that induced by other noradrenaline uptake inhibitors, such as desipramine, cocaine, guanethidine and reserpine. Analysis of the time-course of antagonism by propranolol indicates that it was evident only when the β-adrenoceptor blocking agent remained in the body. The inhibitory effect of phenoxybenzamine on noradrenaline stores reappeared when propranolol was excreted. Propranolol alone did not change cardiac noradrenaline stores or [3H]noradrenaline. It is concluded that the restoration of reflexly increased adrenergic discharge to normal, because of unmasking of spare α-adrenoceptors resulting from β-adrenoceptor blockade by propranolol rather than competition for binding at the active site of phenoxybenzamine, is responsible for the observed antagonism.