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At least 559 records · Page 31Linked to original sources
PubMed1983

A theoretical study on heat production in squid giant axon.

The heat produced by action currents during the upstroke of the action potential in the squid axon has been calculated. Equations were developed and it was demonstrated that the phase plane area, obtained from nerve action potential upstroke, is a measure of the heat liberated at the axoplasmic level. Assuming the Hodgkin and Huxley model, it was possible to show that the axoplasmic heat is a constant fraction of the total Joule heating.

Action Potentials↗
PubMed1995

The concept of calcium concentration microdomains in synaptic transmission.

Ever since the initial measurements of presynaptic calcium currents it has been evident that calcium triggers transmitter release quite rapidly. Several models indicate, as did the initial voltage clamp measurements, that the calcium concentration triggering such release could be very high at the entry site and that this concentration should be very short lasting. In order to determine this time course, calcium entry was studied at the squid giant synapse by imaging light emission from n-aequorin-J, intracellularly injected into the presynaptic terminal. The imaging utilized a video system capable of acquiring 4000 frames per sec. The results indicate that the calcium entry, triggered by action potentials, reaches a peak within 200 musec and has an overall duration of close to 800 musec, closely matching the duration of the presynaptic calcium current determined by voltage clamp results under similar conditions.

Animals↗
PubMed1978

Intracellular pH transients induced by Co2 or NH3.

Experiments are reviewed in which intracellular pH (pHi), during exposure of a cell to CO2- or NH3-containing solutions, not only undergoes an acidification of alkalinization, respectively, but tends to return toward its original value and, upon removal of the test solution, rebounds to a value more alkaline or acid, respectively, than the initial one. A simple physiochemical model is discussed which interprets these observations both qualitatively and quantitatively. In the case of NH3-induced transients, only passive movements seem to take place; in the CO2-induced transients one must postulate an active 'proton pump'. Experimentally verifiable predictions can be made from these models. It is suggested that many physiological effects follow exposure to CO2 or NH3 may be subject to similar transients and rebounds.

Acid-Base Equilibrium↗
PubMed1978

Intracellular buffering.

In the quantification of buffering the distinct roles of bicarbonate and of other buffers must be taken into account. The determination of the total non-bicarbonate buffer value, betaa, in intact tissues is complicated by active pH regulation and by heterogeneity of cytoplasm with respect to betaa, while heterogeneity with respect to pH in vivo could cause errors in estimates made with homogenates. Available estimates of betaa are discussed, as are the individual contributions of proteins, dipeptides and phosphates. A high betaa is appropriate in cells which sometimes have high rates of glycolysis, or which buffer extracellular fluid, but non-protein buffer concentrations can be well below the limits imposed by osmolarity, perhaps because buffering can upset ionic gradients.

Acid-Base Equilibrium↗
PubMed1978

Active control of intracellular pH.

When the interior of a squid giant axon is loaded with acid, the cell responds by extruding that acid in an energy-requiring process. Our results indicate that this acid extrusion is accomplished by exchanging external HCO3- for internal Cl- at the expense of ATP.

Acid-Base Equilibrium↗
PubMed1981

The significance of the linkage between the Bohr and Haldane effects in cephalopod bloods.

This study concerns the physiological implications of the theoretical identity between the Bohr and Haldane effects in the hemocyanin containing blood from the cephalopods Loligo forbesii and Sepia officinalis. The Bohr factor is for both species lower than -1.0. The functional Haldane coefficient (delta ctCO2/delta cHcO2)pH ranges from -2.0 to -0.9 mMCO2/mMO2 in S. officinalis and from -1.2 to -0.7 mMCO2/mMO2 in L. forbesii. This implies for S. officinalis that there may not be enough protons produced from aerobic metabolism to facilitate the release of O2 from HcO2 via the pH sensitivity of this binding. The amount of anaerobically produced protons are predictably of little consequence for release of Hc bound O2 in cephalopods since octopine as the primary product of anaerobic metabolism is a much weaker acid than lactic acid at physiological pH. It is proposed that during burst swimming powered by the ventilatory current, such as practiced by many squids, the overall requirement for ventilation may increase causing a reduced pCO2 and bring the functional Haldane effect below unity. This implies that more H+ are produced by aerobic metabolism than can be found to hemocyanin, hence a shift of the O2 equilibrium curve to the right and improved O2 unloading potential. The advantage of the very large (pH sensitivity) Bohr shift in benthic forms like S. officinalis, both tolerant of and frequently experiencing hypoxic water, may rest with a marked increase in O2 affinity and improved O2 loading in response to respiratory alkalosis produced by hyperventilation.

Animals↗
PubMed1990

Determination of intracellular pH and PCO2 after metabolic inhibition by fluoride and nitrilotriacetic acid.

Mean intracellular pH (pHi) and PCO2 (PiCO2) have been analysed based on pH and total CO2 measurements in tissue homogenates. Tissues were sampled from undisturbed worms (Sipunculus nudus), squid (Illex illecebrosus), trout (Salmo gairdneri), toads (Bufo marinus), and rats. Homogenate metabolism was inhibited by the addition of potassium fluoride and nitrilotriacetic acid (NTA). Model calculations revealed that the influence of dilution, medium buffers, and contamination by extracellular fluids was negligible. In white muscle tissue the resulting pHi values were virtually the same as found in studies using DMO (dimethyloxazolidinedione). If large fractions of mitochondria were present (e.g. in heart muscle), DMO derived pHi values were considerably higher, probably representing overestimates. Homogenate derived pHi values are concluded to represent the effective mean pHi by taking into account pH gradients, and the volumes and buffering of cellular compartments. High time resolution and small variability make this method especially useful to assess rapid changes in pHi, e.g. in exercising animals.

Acid-Base Equilibrium↗