Biomedical subjects

K S Dhalla

Publications and source records attributed to K S Dhalla.

21 records · Page 2Linked to original sources

PubMed1981

Role of phosphatidylinositol in basal adenylate cyclase activity of rat heart sarcolemma.

The adenylate cyclase activity and phospholipid composition were determined in rat heart sarcolemma after treating the membranes with a phosphatidylinositol-specific phospholipase C. Complete hydrolysis of phosphatidylinositol in sarcolemma was associated with a marked loss of the basal adenylate cyclase activity. The recombination of the supernatant with the phosphatidylinositol-depleted membranes was found to reactivate the adenylate cyclase activity. The soluble component(s) in the supernatant, which restored the adenylate cyclase activity, was thermolabile and precipitated by ammonium sulfate. Extensive hydrolysis of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin in sarcolemma with a Clostridium welchii phospholipase C treatment did not affect the basal adenylate cyclase activity. These results suggest that phosphatidylinositol anchors component(s) essential for the expression of basal adenylate cyclase activity to the myocardial cell membrane.

Adenylyl Cyclases↗

PubMed1980

Structure-function relationship in heart sarcolemma.

Dependence on the membrane lipids of sarcolemmal structure as well as functions was examined by incubating isolated rat heart sarcolemma with phospholipase A, C, or D. Conventional as well as negatively stained electron microscope preparations of the treated membranes revealed structural changes. Ca2+ binding and Na+, K+-ATPase activity were depressed following treatment of the membranes with any of the phospholipases whereas Ca2+-ATPase activity was not affected. Adenylate cyclase activity was increased by low concentration (25 micrograms/mg of protein) of phospholipase A, and a definite inhibition of the enzyme was noticed when the concentration of the phospholipase A was increased to 250 micrograms/mg of protein. Phospholipases C and D had no significant effect on the adenylate cyclase activity. Percentage of phospholipids hydrolyzed was more after phospholipase A treatments. These results provide evidence regarding the involvement of lipids in the membrane structure and functions.

Animals↗

PubMedDate not supplied

A biphasic change in contractile proteins during the development of cardiac hypertrophy in pigs.

A non-failing hypertrophy of the left ventricle was produced in the pig heart by supravalvular banding of aorta for 4, 8 and 12 weeks and the myosin and myofibrillar adenosine triphosphatase activities were measured. A significant increase in myosin Ca2+-ATPase activity was seen at 4 weeks of hypertrophy, but at 8 and 12 weeks this activity was significantly decreased compared to sham control. Similar changes were also seen in actin-activated myosin ATPase activities at 4, 8 and 12 weeks of hypertrophy. There were no changes in the K+- and NH4+-EDTA-stimulated ATPAse activities of myosin. Basal ATPase activities of myofibrils were decreased at 4 and 8 weeks of hypertrophy and there was no change in this activity at 12 weeks of hypertrophy. Ca2+ stimulated ATPase activity of myofibrils was significantly increased at 4 weeks, normal at 8 weeks and significantly reduced at 12 weeks of hypertrophy. The changes in ATPase activities were not due to any alterations of proteins by high concentrations of salts during the purification of myosin. The non-hypertrophied right ventricle from the banded animals did not show any change in the basal or Ca2+ stimulated myofibrillar ATPase activities. It is suggested that hypertrophy of the myocardium is accompanied by specific changes in the enzyme activities of the contractile proteins and the biphasic responses may correlate with the functional state of the myocardium subjected to a chronic increase in pressure.

Adenosine Triphosphatases↗