Mechanisms of developmental increase in the sensitivity to ouabain.
In the present study we examined (1) the arrhythmogenic toxicity of ouabain (5 micrograms/kg/min intravenously) in anesthetized guinea pigs of 1-5 days and 3 months of age, and (2) the state of Na+-Ca2+ in the sarcolemmal vesicles isolated from these age groups. Guinea pigs of 1-5 days old tolerated 75% more ouabain than the young adults without significant alteration in the maximal inotropic response. Sodium-dependent 45Ca2+ uptake was substantially lower in the vesicles isolated from hearts of 3-day-old animals, which was characterized by a lower rate of 45Ca2+ uptake (60% Vmax), as compared to the young adults. There was no significant difference in the affinity for 45Ca2+ (Km). The apparent rate of Na+-dependent 45Ca2+ efflux was also lower in the vesicles from 3-day-old guinea pigs. However, the percent extrusion of 45Ca2+ appeared to be unchanged.
Khatter
J C
JC
Department of Medicine, University of Manitoba, Winnipeg, Canada.
Agbanyo
M
M
Navaratnam
S
S
Hoeschen
R J
RJ
D000375:Aging / Q000502:physiology*; D000758:Anesthesia; D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D004562:Electrocardiography; D005260:Female; D006168:Guinea Pigs; D008297:Male; D010042:Ouabain / Q000494:pharmacology*; D012508:Sarcolemma / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D002132:Calcium Radioisotopes; D010042:Ouabain; D012964:Sodium; D002118:Calcium