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R L DeHaan

Publications and source records attributed to R L DeHaan.

At least 55 records · Page 3Linked to original sources
PubMed1976

Ultraviolet-induced alterations of beat rate and electrical properties of embryonic chick heart cell aggregates.

Embryonic heart cell aggregates were irradiated with ultraviolet light at wavelengths between 260 and 310 nm. Spontaneous beat rate was monitored with the aid of a closed-circuit TV camera and, in separate experiments, electrophysiological changes were assayed by intracellular recording. The characteristic response of 7-day aggregates was an increase in spontaneous beat rate to a maximum plateau level, followed by a rather abrupt cessation of beating. Intracellular recordings during irradiation showed a marked decline in the maximum rate of rise, overshoot, and repolarization phase of the action potential, and a significant change in threshold toward zero. The action spectrum for the termination of beating peaked between 290 and 295 nm; it fell off sharply at longer wavelengths and more slowly at shorter wavelengths. The maximum increase in beat rate was increasingly greater for shorter wavelengths and exhibited no peak in the wavelength range investigated. The sensitivity of aggregates to 295-nm light, as measured by the inverse of irradiation time required to terminate beating, decreased with increasing aggregate size and external potassium concentration, was relatively independent of temperature, and increased with embryonic age. The ultraviolet-induced increase in beat rate and termination of beating are attributed to separate complementary processes, a depolarization of the membrane, and a decline in "fast" sodium conductance.

Action Potentials↗
PubMed1975

Amino acid transport by aggregates of cultured chicken heart cells. Effect of insulin.

Single heart cells dissociated from 14-day-old chicken embryos were reagregated into spheroidal clusters on a gyratory shaker and centrifuged to form cohesive discs of approximately 400 aggregates. These cultured cells accumulated 2-amino[1-14C]isobutyric acid against a gradient. When incubated for 3 hours in a protein-free, buffered, balanced salt solution, concentrative transport decreased to a stable basal level. Incubation in the presence of sodium bovine insulin prevented this fall in transport activity and resulted in increased 2-aminoisobutyric acid uptake to concentrations 40 time sthat in the medium during a subsequent 3-hour transport assay. Intracellular accumulation of 2-aminoisobutyric acid was linear during the initial 15 min of transport in the presence and absence of added insulin. Basal transport of 2-aminoisobutyric acid was temperature-dependent, requied extracellular sodium greater than 125 meg/liter, and demonstrated saturation with an apparent Vmax of 3.4 mmol/liter/10 min and an apparent Km of 2.6 mM. Basal transport activity was not reduced by cycloheximide or puromycin even after 3 hours of exposure...

Aminoisobutyric Acids↗
PubMed1973

Ion levels and membrane potential in chick heart tissue and cultured cells.

Intracellular concentrations of sodium and potassium as well as resting potentials and overshoots have been determined in heart tissue from chick embryos aged 2-18 days. Intracellular potassium declined from 167 mM at day 2 to 117-119 mM at days 14-18. Intracellular sodium remained nearly constant at 30-35 mM during the same period. The mean resting potential increased from -61.8 mV at day 3 to about -80 mV at days 14-18. The mean overshoot during the same period increased from 12 to 30 mV. P(Na)/P(K) calculated from the ion data and resting potentials declined from 0.08 at day 3 to 0.01 at days 14-18. Thus, the development of embryonic chick heart during days 2-14 is characterized by a declining intracellular potassium concentration and an increasing resting potential and overshoot. Heart cells from 7- to 8-day embryos, cultured either in monolayer or reassociated into aggregates, were compared with intact tissue of the same age. The intracellular concentrations of sodium and potassium were similar in the three preparations and cultured cells responded to incubation in low potassium medium or treatment with ouabain in a manner similar to that of intact tissue. Resting potentials and overshoots were also similar in the three preparations.

Animals↗
PubMed1973

Tetrodotoxin desensitization in aggregates of embryonic chick heart cells.

Spontaneous beating of heart-cell aggregates from 4-day chick embryos was initially blocked by 10(-5) g/ml tetrodotoxin (TTX). With continued exposure to the drug, the fraction of blocked aggregates decreased from about 80% at 15 min to about 25% at 2-3 h, at which time, beating aggregates had become desensitized to the toxin, showing no response to a fresh dose. Aggregates from 5-day hearts were more sensitive to TTX, but fewer became desensitized in its presence. Desensitization to TTX was not seen in 6- and 7-day aggregates. Inhibition of protein synthesis by cycloheximide did not affect beating or initial sensitivity to TTX of 4-day aggregates, but desensitization failed to occur. Before TTX, the mean value of maximal upstroke velocity (V(max)) of the action potentials in 4-day aggregates was 33 V/s. After desensitization V(max) was 12 V/s. Activity of desensitized aggregates in the presence of TTX was augmented by elevated calcium levels, and suppressed by presumed inhibitors of slow inward current (manganese, D600). Desensitization was reversible; upon removal of TTX 10(-5) g/ml, aggregates regained their responsiveness to a fresh dose of the drug with a 2-3 h time-course similar to that of desensitization. This was prevented by continued exposure to TTX at concentrations as low as 10(-8) g/ml. These data suggest that (a) desensitization involves a change in the mode of action-potential generating from one involving Na-specific, TTX-sensitive channels to one utilizing slower Mn-sensitive channels; (b) the process of desensitization occurs over a period of 2-3 h and is dependent upon the products of protein synthesis; and (c) desensitization is reversible after removal of TTX over a 2-3 h time-course similar to its onset.

Action Potentials↗
PubMed1972

Development of sensitivity to tetrodotoxin in beating chick embryo hearts, single cells, and aggregates.

The spontaneous activity of intact embryonic heart becomes progressively more sensitive to tetrodotoxin block with increasing age of the embryo. The activity of isolated single heart cells in culture was relatively insensitive, independent of embryo age. Aggregates formed from single cells responded to tetrodotoxin in the same manner as intact hearts; aggregated cells from older hearts were sensitive.

Animals↗
PubMed1968

The electrical activity of embryonic chick heart cells isolated in tissue culture singly or in interconnected cell sheets.

Embryonic chick heart cells were cultured on a plastic surface in sparse sheets of 2-50 cells mutually in contact, or isolated as single cells. Conditions are described which permitted conjoint cells to be impaled with recording microelectrodes with 75 % success, and isolated single cells with 8 % success. It is proposed that cells in electrical contact with neighbors are protected from irreversible damage by the penetrating electrode, by a flow of ions or other substances from connected cells across low-impedance intercellular junctions. Action potentials recorded from conjoint and isolated single cells were similar in form and amplitude. The height or shape of the action potential thus appears not to depend upon spatial relationships of one cell to another. As the external potassium concentration was increased from 1.3 mM to 6 mM, cells became hyperpolarized while the afterhyperpolarization was reduced. At higher potassium levels, the afterhyperpolarization disappeared, the slope of the slow diastolic depolarization decreased, and resting potential fell along a linear curve with a slope of 61 mv per 10-fold increase in potassium. In pacemaker cells the diastolic depolarization consists of two phases: (a) recovery from the afterpotential of the previous action potential and (b) the pacemaker potential. These phases are separated by a point of inflection, and represent manifestations of different mechanisms. Evidence is presented that it is the point of inflection (PBA) rather than the point of maximal diastolic potential, that should be taken as the resting potential.

Action Potentials↗