Influence of myosin antibodies on heart sarcolemmal Ca2+-dependent ATPase

65 NATRIURETIC FACTOR IN ISOLATED RAT ATRIAL MYOCYTES. N.C. Ochsner Medical Trippodo, A.A. MacPhee, F.E. Cole. Institutions, New Orleans, LA 70121 Rat atriai natriuretic-factor (ANF),extracted in acid, elutes from Sephadex G-75 in the 5-30 K dalton range, whereas when the pH of the extract is adjusted to 8.2, ANF elutes in Atria from 30 Sprague-Dawley rats the 5 K (or less) range. were homogenized in 1.0 M acetic acid, lyophilized and fractionated on Sephadex G-75 in 0.5 M acetic acid. The 5-30K eluate was lyophilized, dissolved in phosphate buffered saline (PBS) and divided into four aliquots: untreated (control), heated to 1000 for 10 min, incubated with concanavalin, or Natriuretic activity (NA) was deterincubated with trypsin. mined by injecting the samples at 4 ml/kg into assay rats. The % change in sodium excretion (%AUNaV) following injection as compared with the average of three lo-min control periods were 1,015 + 400, 1,765 + 679, 734 + 216 and 52 + 33 (+ SE) for control, heated, concanavalin and trypsin samples, respectively (p< 0.05 for all except trypsin). Rat atria1 myocytes were isolated by perfusing fresh rat hearts with collagenase solution. Acid extracts of the myocytes and perfusion medium were gel filtered, lyophilized, dissolved in PBS and assayed as before. UNaV increased by 1110% after injecting myocyte extract and only 15% after injecting perfusion medium "extract." The results suggest that ANF is localized within Supported in part atria1 myocytes and not extracellularly. by dL 23157.

INFLUENCE OF MYOSIN ANTIBODIES ON HEART SARCOLEMMAL Ca2+-DEPB.S. Tuana, M.J.B. Kutryk, 3. Wikman-Coffelt ENDENT ATPase. and N.S. Dhalla. Faculty of Medicine, University of Manitoba Winnipeg, Canada R3E OW3 2+ Although the presence of Ca -dependent ATPase in sarcolemma1 membrane has been demonstrated, very little is known regarding the nature of this enzyme. In order to gain information if this enzyme exhibits myosin-like characteristics, the effect of dog heart myosin antibodies was studied on the dog heart sarcolemmal Ca2+-dependent ATPase. The data indicated that Ca2+-dependent ATPase of sarcolemma was inhibited by about 25% at the myosin antibody concentration which decreased Ca2+-stimulated ATPase of myofibrils by 75-80%. Unlike sarcolemma1 Ca2+-dependent ATPase, the depression of myofibrillar Ca2+-stimulated ATPase by myosin antibodies was independent of the preincubation time. The basal myofibrillar ATPase activity was increased whereas Mg 2+ ATPase activity in sarcolemma was moderately inhibited by myosin antibodies. Dog heart Na+K+ ATPase antibodies which decreased markedly the sarcolermnal Na+-K+ ATPase activities,also inhibited the sarcolemmal Ca2+dependent ATPase and Mg2+ ATPase activities by lo-15%. Ca2+dependent ATPase solubilized from sarcolemma and ourified myosin ATPase were depressed by 28 and 76% by myosin antibodies. The results of this study provide some evidence to distinguish sarcolemmal Ca2f-dependent ATPase from myosin ATPase. (Supported by a grant from the Medical Research Council).