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Biomedical subjects

G D Webb

Publications and source records attributed to G D Webb.

At least 73 records · Page 4Linked to original sources
PubMed1987

Congenital heart disease in pregnancy: short- and long-term implications.

One hundred forty-four pregnancies that occurred in 74 patients with congenital heart disease at the Toronto General Hospital between 1975 and 1986 were reviewed. The patients were divided into two groups, those with acyanotic lesions and those with cyanotic lesions. Maternal and fetal outcomes in these two groups were compared. Patients with cyanotic lesions developed significantly more congestive heart failure and deteriorated more often in functional cardiac status than those with acyanotic lesions (p less than 0.005). Women with obstructive lesions had a higher incidence of pregnancy-induced hypertension than our general population (p less than 0.005). There was one maternal death in the puerperium in a woman with Eisenmenger's syndrome. Preterm births were more frequent in the cyanotic group (p less than 0.01) as were small for gestational age infants (p less than 0.005). In the cyanotic group the mean birth weight was 900 gm less than that in the acyanotic group (p less than 0.005). The major benefits of corrective cardiac surgery were in the cyanotic group and consisted of fewer spontaneous abortions (p less than 0.01) and small for gestational age infants (p less than 0.02) and more term births (p less than 0.01). Long-term follow-up revealed that 19.2% of women with acyanotic lesions had significant cardiac developments, compared with 90% in the cyanotic group (p less than 0.005). One of 87 infants (1.1%) had congenital heart disease and two had Marfan's syndrome.

Female↗
PubMed1980

The effects of external Ca++ and Mg++ on the voltage sensitivity of desensitization in Electrophorus electroplaques.

Desensitization onset was studied in voltage-clamped Electrophorus electroplaques during prolonged exposure to bath-applied carbamylcholine. The time-course of desensitization was described by a first-order rate constant kappa obs, which increased exponentially with membrane hyperpolarization from -20 to -90 mV. When Ca++ was increased from 2 to 10 mM, the voltage sensitivity of kappa obs decreased; kappa obs decreased for voltages more negative than -40 mV, and increased slightly at voltages more positive than -40 mV. 10 mM Mg++ had a less pronounced effect and the voltage sensitivity of kappa obs was unchanged. The equilibrium level of desensitization, estimated from the carbamylcholine-dependent conductance which remained after desensitization was apparently complete, also increased with hyperpolarization.

Action Potentials↗
PubMed1977

Interactions of lanthanum with purified and intact cell acetylcholinesterase of Electrophorus electricus.

The effects of lanthanum on the activity of purified preparations of acetylcholinesterase (AChE) from the electric organ of E. electricus and on the activity of AChE in intact electroplaques from the same species were studied. 0.1 mM LaCl3 produced an initial inhibition of purified AChE which was followed by a delayed activation of the enzyme. Upon pretreatment of purified enzyme with LaCl3, initial activity was markedly increased. LaCl3 exerted a marked, concentration-dependent inhibition of intact cell AChE. La3+ and Ca2+ appear to interact competitively. In the presence of both 10 mM CaCl2 and 0.1 mM LaCl3, the initial activitity of purified AChE was increased at lower ACh concentrations and inhibited at ACh concentrations greater than 3 X 10(-4) M. Inhibition of intact cell enzyme by 0.1 mM LaCl3 was relieved by increasing the CaCl2 concentration to 10 mM at ACh concentrations less than 2 X 10(-4) M. The data were analyzed assuming Michaelis-Menten kinetics and interpreted with reference to the differential binding of divalent and trivalent cations to regulatory anionic sites which are separate and distinct from the anionic site of the active center of the enzyme.

Acetylcholine↗
PubMed1977

Rapid desensitization of acetylcholine receptors of eel electroplaques following iontophoretic application of agonist compounds.

1. The electrical potential difference across the innervated membrane of the electroplaque of Electrophorus electricus was measured with an intracellular micro-electrode while an extracellular double-barrelled micropipette was used to apply acetylcholine and carbamylcholine iontophoretically very close to the point of insertion of the recording electrode. 2. The average depolarizing response to brief (several msec) pulses of carbamylcholine decayed 22 times more slowly than the response to acetylcholine. Treatment of the electroplaque with eserine or neostigmine prolonged the acetylcholine responses. 3. When a steady current of acetylcholine was applied for several seconds, the membrane first depolarized, then partially repolarized. Usually no repolarization was seen during long pulses of carbamylcholine or long pulses of acetylcholine in the presence of eserine or neostigmine. 4. During long conditioning pulses of acetylcholine or carbamylcholine, the responses to brief test pulses of acetylcholine showed a progressive decline in amplitude, but recovered after termination of the conditioning pulse. Desensitization half-times as short as 0-6 sec were observed, making these results similar to those obtained in the frog motor end-plate.

Acetylcholine↗