Effects Of Changes In Extracellular pH Research Articles

The Effect of Extracellular pH Changes on Intracellular pH and Nitric Oxide Concentration in Endothelial and Smooth Muscle Cells from Rat Aorta

AimsIt has been known for more than a century that pH changes can alter vascular tone. However, there is no consensus about the effects of pH changes on vascular response. In this study, we investigated the effects of extracellular pH (pHo) changes on intracellular pH (pHi) and intracellular nitric oxide concentration ([NO]i) in freshly isolated endothelial cells and cross sections from rat aorta.Main MethodsThe HCl was used to reduce the pHo from 7.4 to 7.0 and from 7.4 to 6.5; the NaOH was used to increase the pHo from 7.4 to 8.0 and from 7.4 to 8.5. The fluorescent dyes 5-(and-6)-carboxy SNARF-1, acetoxymethyl ester, acetate (SNARF-1) and diaminofluorescein-FM diacetate (DAF-FM DA) were employed to measure the pHi and [NO]i, respectively. The fluorescence intensity was measured in freshly isolated endothelial cells by flow cytometry and in freshly obtained aorta cross sections by confocal microscopy.Key FindingsThe endothelial and vascular smooth muscle pHi was increased at pHo 8.5. The extracellular acidification did not change the endothelial pHi, but the smooth muscle pHi was reduced at pHo 7.0. At pHo 8.5 and pHo 6.5, the endothelial [NO]i was increased. Both extracellular alkalinization and acidification increased the vascular smooth muscle [NO]i.SignificanceNot all changes in pHo did result in pHi changes, but disruption of acid-base balance in both directions induced NO synthesis in the endothelium and/or vascular smooth muscle.

Intracellular microelectrode membrane potential measurements in tobacco cell-suspension protoplasts and barley aleurone protoplasts: interpretation and artifacts

Intracellular microelectrode measurements in plant cell protoplasts have been widely used to study hormone signal transduction processes. However, the interpretation and reliability of such measurements are largely dependent on a detailed evaluation of the measurement conditions, as investigated in the present paper. Upon microelectrode penetration of tobacco cell suspension protoplasts and of barley aleurone protoplasts a fast negative going impalement-induced potential transient of less than a few ms duration could be observed. After reaching a steady-state potential at the ms time scale the measured potential hyperpolarized again and, in most cases, subsequently depolarized to a new steady-state value. Analysis of the electrical equivalent circuit of the measurement configuration showed that the occurrence of the impalement-induced potential transient indicates that these measurements suffer from a microelectrode-induced shunt resistance which loads the measurement. In addition, it is shown that the peak-value of the potential transient is the most reliable indicator of the true membrane potential and of true membrane potential changes of the protoplast, since this value is rather membrane resistance independent. For correct interpretation of steady-state measurements of membrane potential and stimulus-induced membrane potential changes data on membrane and shunt resistance are essential. As an example of the measurement of membrane potential changes the effects of 1-NAA on measured potential values in tobacco protoplasts and the effect of extracellular pH changes on barley aleurone protoplasts are analyzed with regard to the above described conclusions.

Neurons sensitive to pH in slices of the rat ventral medulla oblongata

The effects of extracellular pH changes on neurons in slices of the rat ventral medulla oblongata were investigated by extracellular recording. Changes in discharge rate were correlated with pH changes in the tissue next to the recorded cell, as measured by H(+)-selective microelectrodes. pH was altered by varying the bicarbonate concentration ([HCO3-]) in the superfusion solution. In 136 out of 316 neurons, the number of spontaneous or electrically evoked discharges per unit time increased with decreasing pH and decreased with increasing pH. Changes of only 0.01-0.04 pH unit were effective in these pH-sensitive neurons. The response was transient; the discharge rate returned to the control value within a few minutes. The pH sensitivity persisted in the presence of 0.5 microM atropine, 20 microM bicuculline and after replacing Ca2+ by Mg2+ in the superfusion solution to reduce synaptic transmission. The response to the same pH decrease was stronger when increasing PCO2 than when reducing [HCO3-]0. The pH-induced response significantly increased during hypoxia. The results show that in the ventral medulla oblongata neurons exist that transiently respond to small decreases and increases of pH. The pH sensitivity is an intrinsic property of these neurons; it is not due to a synaptic mechanism but is modulated by PCO2 and PO2.

The voltage dependence of the chloride conductance of frog muscle.

1. The effect of extracellular pH changes on the voltage-current relation of frog muscle membrane has been studied using intracellular microelectrodes. To reduce the cation conductance of the membrane, potassium in Ringer solution was replaced by rubidium.2. When the relatively impermeant methyl sulphate ion replaced extracellular chloride the membrane conductance was low, time independent and little influenced by extracellular pH changes. The voltage-current relation was linear at both high and low pH values.3. In rubidium Ringer solution at pH 7.4 the membrane conductance fell as the inside of the fibre was made more negative, in a manner consistent with the predictions of the constant field theory.4. At a high pH value (9.8) the resting conductance was high, but it fell steeply as the membrane potential was increased; for large hyperpolarizing voltages the membrane current tended to a limiting value. The voltage-current relation crossed those recorded at pH 7.4 and 5.0.5. In acid Ringer solution (pH 5.0) the resting membrane conductance was low and remained constant until the membrane potential was hyperpolarized more than 30 mV beyond the resting value; the conductance then rose as the membrane potential was further increased. For large hyperpolarizations the membrane conductance was higher at pH 5.0 than at pH 9.8.6. Experiments using two successive, identical, constant current pulses suggested that the membrane conductance altered during the passage of current across the membrane; in alkaline solution the conductance fell with time, in acid solution it rose.7. Because no time or voltage dependence of the membrane conductance was seen in the absence of chloride ions it is inferred that the movements of chloride ions across the muscle membrane are responsible for both the time and voltage dependent alterations in membrane conductance seen at different pH values.