Phospholipid composition and amphiphile content of isolated sarcolemma from normal and autolytic rat myocardium

Caprine cardiac sarcoplasmic reticulum isolation and biochemical characterisation with emphasis on Ca(2+)-adenosine triphosphatase

This study was aimed at isolating, in its pure form, and characterizing the sarcoplasmic reticulum from caprine (Capra hircus) heart. The sarcoplasmic reticulum from thirty caprine heart ventricular homogenates was isolated and purified. It was characterized on the basis of both, its protein and lipid composition. The protein content was 142±10 mg/g of tissue. Ca(2+)-ATPase activity equaled 3.75±1.06mmol Pi/mg protein/min while the uptake rate was 24±1.14 nmol/mg protein/min. 205kD, 110kD, 90kD, 84kD, 66kD, 55kD and 29kD molecular weight proteins were seen on an SDS polyacrylamide gel. Triglyceride, Cholesterol and Phospholipids (phosphatidylethanolamine, phosphatidylinositol, phosphatidylcholine, sphingomyelin and phosphatidylserine) were present in increasing order of their concentration. Long chain fatty acids predominated over the unsaturated ones. The ryanodine receptor displayed two binding sites for ryanodine. Characterisation encompassing the above biochemical aspects of normal caprine cardiac sarcoplasmic reticulum was thus achieved after isolating it in the pure form.

The modulatory effects of endothelin-1, carbachol and isoprenaline upon Na(+)-H+ exchange in dog cardiac Purkinje fibres

1. The modulatory effects of carbachol, endothelin-1 and isoprenaline upon Na(+)-H+ exchange were examined in dog cardiac Purkinje fibres. Intracellular pH (pHi) and intracellular sodium activity (aiNa) were recorded using pH and Na(+)-selective microelectrodes. Acid extrusion via Na(+)-H+ exchange was estimated from the pHi recovery rate (multiplied by intrinsic buffering power (beta i) and adding mean background acid load) in response to an internal acid load induced by the removal of 20 mM NH4Cl. All experiments in this work were performed in Hepes-buffered solutions at 37 degrees C. 2. beta i was estimated at various values of pHi in the range of 7.4-6.4 and was calculated from the fall of pHi induced by the addition and removal of NH4Cl. Experiments were performed when Na(+)-H+ exchange was blocked. The values of beta i in this tissue were only slightly dependent on pHi in the range of 7.4-6.4 with an empirical relationship: beta i = -4.69 pHi + 64.59. 3. Endothelin-1 (10(-8) M) alkalinized the resting pHi by approximately 0.1 pH unit and accelerated acid extrusion, by approximately 96%, at pHi approximately 6.9. A reduction of background acid loading within the cell cannot account for the augmentation of pHi recovery, since the rate of acid extrusion was not changed either at resting pHi or at internal acidification in Na(+)-free solution (a measure of background loading) by the addition of endothelin-1. The protein kinase C inhibitors staurosporin (10(-6) M) and 1-(5-isoquinolinylsulphonyl)-2-methyl-piperazine (H-7, 50 microM) could not block the effect of endothelin-1 on the antiporter. 4. At pHi approximately 6.8, carbachol (7.5 x 10(-4) M) accelerated pHi recovery by approximately 68% and alkalinized the resting pHi by approximately 0.1 pH unit. This stimulatory effect of carbachol was completely blocked by pretreatment with atropine (10(-4) M) and staurosporine 10(-6) M. The background acid load was not reduced by adding carbachol, since the acid extrusion during pHi recovery or at the resting state was not affected by the addition of carbachol to a sodium-free solution. 5. Isoprenaline (10(-6) M) slowed pHi recovery by approximately 45% measured at pHi 6.9 with no change in resting pHi. A rise in background acid loading could not account for the reduction of acid extrusion. Pretreated with atenolol (10(-6) M), a beta 1-selective antagonist, completely blocked the effect of isoprenaline.(ABSTRACT TRUNCATED AT 400 WORDS)

Anoxic injury accelerates phosphatidylcholine degradation in cultured cardiac myocytes by phospholipase C

In neonatal cultured cardiac myocytes under normoxic conditions, 32Pi incorporation pattern into various phospholipids, and double-labeling experiments with 32Pi and [3H]methyl choline, suggest that phosphatidylcholine and phosphatidylinositol are turned over rapidly, whereas the turnover of phosphatidylethanolamine is probably much slower. While increased levels of the corresponding lysophospholipids were not found under anoxia, release of diacylglycerol and phosphorylcholine was observed. These data strongly suggest that phospholipase C, and not phospholipase A2, is involved in phospholipid degradation in cultured cardiomyocytes under anoxic conditions.

Anti-ischemic and membrane stabilizing activity of calmodulin inhibitors

In the control perfused working rat hearts subjected to 25 min global ischemia, reperfusion resulted in a 50% recovery of the hemodynamic functions. A concentration-dependent improvement of this recovery and a reduction of the postischemic lactate dehydrogenase (LDH) release was caused by calmidazolium (CMZ), trifluoperazine (TFP), and chlorpromazine (CPZ) added prior to ischemia. The drugs were not effective when added only to the reperfusate. The concentrations of CMZ, TFP, and CPZ producing the half-maximal effects were 2.5 X 10(-9) M, 1.5 X 10(-7) M and 3 X 10(-7) M, respectively. Prolongation of the ischemic period caused a progressive deterioration of the functional recovery of the hearts while the total postischemic LDH release showed, at the same time, an initial gradual rise followed by a later decay. In untreated hearts the duration of ischemia resulting in 50% loss of hemodynamic function and in a maximal LDH release was 25 min. TFP (10(-6) M) and CMZ (10(-7) M) prolonged these times by 4-7 min and 5-10 min. respectively. TFP, CPZ, and CMZ protected the erythrocytes from osmotic hemolysis. The maximum anti-hemolytic activity was produced by 3 X 10(-6) M CMZ, 3 X 10(-5) M TFP, and 10(-4) CPZ. The concentration-dependency of this effect was not affected by low concentrations of sodium dodecyl sulphate (SDS). Neither TFP nor CMZ prevented the hemolysis produced by 10(-3) M SDS. It is concluded that the delay in the development of the ischemic injury produced by TFP and CMZ is due to the effects of these drugs as calmodulin antagonists rather than as membrane stabilizers.