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Biomedical subjects

P Prakash

Publications and source records attributed to P Prakash.

At least 37 records · Page 2Linked to original sources
PubMed1996

Effects of calcium channel blockers on spontaneous electrical activity of freshly isolated three-day-old embryonic chick ventricle.

The effects of four major types of organic Ca2+ channel blockers, verapamil, nifedipine, diltiazem and fendiline and of tetrodotoxin (TXX), a fast Na+ channel blocker, on the action potential (AP) of freshly isolated 3-day-old embryonic chick ventricle (3d ECV) were investigated to resolve the controversy about the ionic basis of upstroke. The APs were characterized by a maximum diastolic potential (MDP) of -60 mV, an overshoot (Eov) of 16 mV and a maximum upstroke velocity (+Vmax) of 42 V s-1. All four Ca2+ channel blockers (0.1-40 microM) and TTX (0.1-80 nM) produced a dose-dependent reduction in +Vmax and Eov. MDP was also reduced by Ca2+ channel blockers in a dose-dependent manner but was unaffected by TTX. A significant linear correlation between MDP and +Vmax was observed for verapamil (r = 0.99), nifedipine (r = 0.99), diltiazem (r = 0.96) and fendiline (r = 0.98). Surprisingly, all Ca2+ channel blockers produced a dose-dependent positive chronotropic effect leading to cessation of firing at high doses (20-40 microM). In preparations becoming quiescent with high doses of verapamil (20-40 microM), elevated extracellular concentrations of Ca2+ (up to 9.6 nM) and isoproterenol (0.5-40 microM) failed to restore spontaneous APs. Electrical stimulation also failed to elicit APs in preparations inhibited by verapamil, diltiazem and fendiline. The inhibition of +Vmax by TTX demonstrates that fast Na+ channels were involved in the upstroke of AP in 3d ECV. Voltage-dependent inactivation of fast Na+ channels during depolarization (reduction in MDP) by the Ca2+ channel blockers explains their inhibitory effect on +Vmax and indicates that L-type Ca2+ channels had no significant role in the upstroke. A positive chronotropic effect of the Ca2+ channel blockers further suggests that slow Ca2+ channels are not involved in automaticity in freshly isolated 3d ECV.

Action Potentials↗
PubMed1995

A study of platelet alloantibody in multiply-transfused haematology patients.

This paper studies the prevalence of platelet antibody in multiply-transfused leukaemia and other transfusion-dependent non-leukaemic patients, using a solid phase red cell adherence (SPRCA) assay and a microlymphocytotoxicity (LCT) test. A positivity rate of 26% in the leukaemic patients and 72% in non-leukaemic patients was obtained with the SPRCA assay, compared to a higher positivity rate of 69% and 83% in the respective groups using the LCT test. Several explanations are proposed. The lower sensitivity of the SPRCA assay suggests that the LCT test may need to be run concurrently for higher diagnostic yield. This paper also compares the performance between an in-house SPRCA test method and the commercial Capture P test kit, and good concordance was shown in repeated occasions.

Antigens, Human Platelet↗
PubMed1995

Effect of monocular vertical displacement of horizontal recti in A V phenomena.

Twenty-one cases of A V phenomena were subjected to monocular recession-resection procedure with vertical displacement of 8 mm in 11 cases and 5 mm in 10 cases. Both 8 mm and 5 mm shifts were found to be equally effective even in cases with mild or moderate cyclovertical muscle imbalance. However, in cases with oblique muscle dysfunction, residual vertical incomitance was observed in all such 13 cases and should therefore be avoided. Eight cases showed horizontal incomitance in extreme gazes and this was more with 8 mm shift compared to 5 mm shift.

Eye Movements↗
PubMed1994

Pure anteropositioning of inferior oblique. A selective weakening procedure.

Anteropositioning of inferior oblique is of late becoming popular but it inadvertently also entails a compulsory recession which may be undesirable at times. We have evaluated the effect of a 'pure' anteropositioning procedure (11 eyes), with Elliot & Nankin's anteropositioning (10 eyes) and Parks' recession (17 eyes). The mean change of vertical deviation in elevation in adduction (surso adduction) was 15.09 +/- 8.3 prism dioptres (p.d.) in pure anteropositioning; 23.50 +/- 5.6 p.d. in E & N's anteropositioning and 14.82 +/- 5.9 p.d. in Parks' recession, showing this procedure to be as effective as a conventional recession procedure. However, while the latter two methods produced an intorsion, 'pure' anteropositioning produced no significant change in torsion. It is a much simpler procedure to weaken the elevation without affecting the torsion.

Eye Movements↗
PubMed1993

Saccadic underaction in concomitant strabismus and Hering's law: a new neurophysiologic model for binocular motor correspondence.

Hering's law of equal innervation has remained so far as an universal truth with no scientific basis. However, recent reports of Saccadic underactions in concomitant strabismus indicating asymmetric ocular motor innervation is in contradiction to the law. In an effort to understand the inequalities of binocular movements, we propose a neurophysiologic model for both normal and abnormal eye movements. The model hypothesizes that any binocular movement results from the yoking of two monocular reflex loops corresponding to the two eyes, during the plastic stage of development of ocular motor reflexes. The retinal target discrepancy triggers the reflex loop resulting in a monocular corrective movement. As there is a common binocular field, the stimuli to the two eyes are similar causing a similar binocular corrective movement. In abnormal cases coupling of asymmetric motor loops may occur resulting in alternate or unilateral saccadic underactions.

Electrooculography↗
PubMed1993

Morphological identification of Candida species on glucose agar, rice extract agar and corn meal agar with and without Tween-80.

A comparative study for the identification of 32 known strains of Candida species on the basis of morphology on glucose agar, rice extract agar and corn meal agar with and without Tween 80 revealed that when Tween 80 is incorporated in the media identification is possible for 96.8% of the species within 48 hours on rice extract agar and for 96.8% of the species within 48 hours on rice extract agar and for 90.6% of the species on glucose agar. The germ tubes and chlamydospores were also produced more on rice extract agar than on 0.1% glucose agar. Rice extract agar with Tween 80 can be used as single medium for morphologic identification of Candida species. The inoculated medium is first incubated at 37 degrees C for 3 hours and examined for germ tube formation and then incubated at 25 degrees C for 24 to 72 hours and examined for appearance of chlamydospores and mycelial morphology.

Agar↗
PubMed1992

45Ca-efflux in embryonic chick heart and its modification by caffeine and ryanodine.

Ontogenic changes in the kinetics of exchangeable cellular calcium were studied in embryonic (ECV) and post-hatch (PHCV) chick ventricular tissue by monitoring 45Ca-efflux. The isolated whole ventricle (5 & 7 days ECV) or ventricular strips (12 & 18 days ECV and 1-2 days PHCV) were "loaded" with 45Ca (37 degrees C) and then passed through a series of tubes containing efflux solution (4 degrees C) to determine 45Ca-efflux. Curve 'peeling' of the efflux curve indicated existence of 3 kinetically distinct components of exchangeable cellular Ca2+ compartments: C1, C2 & C3. The size of C1, which was the largest in 5 & 7 days ECV decreased significantly to become minimum in 18 days ECV & PHCV. The rate constant of this compartment, however, reduced with the age of the embryo. In contrast, the size of C3 increased with the embryonic development to become the largest in 18 days ECV & PHCV. An increase in the rate constant of this compartment was also observed during embryogenesis. The size and rate constant of C2 remained unaltered during development. However, the increase in size of C3 during embryonic development indicates differentiation of Ca2+ storage sites, like sarcoplasmic reticulum (SR), during the later stages. Caffeine (10 mM) and ryanodine (10 microM) enhanced fractional escape rate during slow phase (ie 120-180 min) of efflux at all developmental stages. The magnitude of enhancement increased during later stages of development indicating greater prominence of SR with the age of embryo.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Enriched collagen as coadjuvant therapeutic agent in experimental osteomyelitis in dogs.

Osteomyelitis was induced in the tibiae of dogs by injecting hemolytic strain of Staphylococcus aureus. Clinical, radiological and histomorphological reactions in the diseased tibiae were studied up to 15 weeks to evaluate the response of infected bone to parenteral oxytetracycline in cases of closed wounds and surgical curettage, antimicrobial irrigation along with parenteral oxytetracycline therapy in animals carrying open wounds. Enriched collagen as a constituent of therapeutic regimen was also administered locally and its efficacy during resolution of osteomyelitis was compared with other treatments. Surgical curettage along with irrigation of lesions was observed to be an effective method for bringing an early recovery in aggravated cases of osteomyelitis. The addition of collagen enhanced the healing process in comparison with non-collagen treated animals.

Adjuvants, Pharmaceutic↗
PubMed1990

The vasopressin response to severe birth asphyxia.

Serial measurements of urinary arginine vasopressin (AVP) were made in six severely birth asphyxiated newborn infants. In five infants serial plasma concentrations were also evaluated. There was a strong negative correlation between plasma AVP and plasma osmolality in these infants (r = -0.52, P = 0.0012). In neither the individual babies nor the group as a whole was there a significant correlation between plasma AVP and the urinary excretion of AVP even if the latter was standardised for creatinine content. Normal development at follow up was only observed in two asphyxiated infants who had consistently low urinary arginine vasopressin levels in the first days of life. Infants with consistently high urinary vasopressin concentrations either died or were severely abnormal in their subsequent development.

Apgar Score↗
PubMed1990

Scleral dellen in strabismus surgery.

This communication highlights scleral dellen as an unusual complication of strabismus surgery in a 55-year-old hypertensive male. The clinical significance, differential diagnosis and management of this condition has been discussed.

Humans↗
PubMed1990

Air leaks and vasopressin release.

Eleven very low birthweight babies being ventilated for respiratory problems during the first week of life developed air leaks on 22 occasions. On 16 out of 19 occasions the infants showed increases in urinary excretion of vasopressin after these events and on 10 occasions out of 13 there was a rise in the plasma arginine vasopressin concentration. The peripheral signs of the syndrome of inappropriate antidiuretic hormone release were seen on only one occasion in response to the sometimes high vasopressin concentrations.

Arginine Vasopressin↗
PubMed1987

Saccadic eye velocity in concomitant divergent squint.

Study was conducted on 10 normal subjects, 20 cases of unilateral divergent squint and 20 cases of alternating divergent squint. In unilateral divergent squint cases lateral rectus of nondominant eye showed overactivity on fixation with dominant eye. In the alternating divergent squint cases which had onset of squint at or after the age of 2 years showed increased saccadic velocity of medial rectus of non-dominant eye on fixation with dominant eye. Working hypothese have been suggested to explain these phenomena.

Eye Movements↗