Charles A. Napolitano

Direct determination of the calcium profile structure for dipalmitoyllecithin multilayers using neutron diffraction

The distribution of calcium in lamellar phases of dipalmitoyllecthin (DPPC) multilayers was directly determined by neutron diffraction and stable isotope substitution of 44Ca for 40Ca. A significant resonance effect on the intensities of the lamellar diffraction pattern was observed for millimolar concentrations of these calcium isotopes. The calcium difference profile indicated that calcium was localized in the phospholipid headgroup region, being excluded from the hydrocarbon core as was water separately determined from the water profile structure obtained by H2O/D2O exchange. A reciprocal space analysis of the difference structure factors indicated that calcium binds preferentially to within 1-2 A of the phosphate moiety of the phospholipid head groups of the DPPC bilayer.

Organization of calcium pump protein dimers in the isolated sarcoplasmic reticulum membrane

The arrangement of the calcium pump protein in the isolated sarcoplasmic reticulum (SR) membrane was examined by optical diffraction of freeze-fracture electron micrographs. Several states of protein particle organization were observed: random, hexagonal and tetragonal packing, and a mixture of hexagonal and tetragonal packing. This suggests that the time-averaged positions of protein particles in the plane of the SR membrane are weakly defined. In addition, there appears to be a greater degree of local or short-range order compared to long-range order within the field of freeze-fracture particles. We utilized measurements from tetragonally or hexagonally packed arrays to determine a unit cell area occupied by each freeze-fracture particle and its associated lipid matrix. When these unit cell areas and the stereologically determined area per freeze-fracture particle were compared to the cross-sectional area occupied by a single calcium pump protein and its associated lipid, obtained by x-ray and neutron diffraction methods, we concluded that each freeze-fracture particle probably represents a dimer of pump protein molecules in the plane of the SR membrane.

Ionic basis of the differential effects of Intravenous anesthetics on erythromycin-induced prolongation of ventricular repolarization in the guinea pig heart

Background: Dysrhythmias and death occur in patients with acquired long QT syndrome (LQTS). Little information exists regarding interactions between anesthetics and drugs that prolong ventricular repolarization. Therefore the effects of three commonly used intravenous anesthetics on ventricular repolarization were investigated in the setting of drug‐induced, long QT syndrome. Methods: The effects of increasing concentrations (0, 10, 25, and 50 micro Meter) of propofol, ketamine, and thiopental on ventricular repolarization were evaluated by measuring the monophasic action potential duration at 90% repolarization (MAPD90) in guinea pig Langendorff‐perfused hearts in the absence or presence of erythromycin (100 micro Meter). If an anesthetic enhanced erythromycin‐induced prolongation of MAPD90, its effects on the delayed rectifier (IK) and inward rectifier (IKl) potassium currents were measured using the whole‐cell patch‐clamp technique. Results: At clinically relevant concentrations, only thiopental significantly modulated erythromycins effect on MAPD90. Thiopental at 10, 25, and 50 micro Meterr prolonged MAPD90 from a control of 163 +/‐ 6 ms by 18 +/‐ 4, 30 +/‐ 3, and 31 +/‐ 4 ms, respectively. In a separate group, erythromycin prolonged MAPD90 from 155 +/‐ 2 ms to 171 +/‐ 2 ms (n = 21, P < 0.001). In the presence of erythromycin, thiopental at 10, 25, and 50 micro Meter caused significantly greater prolongation from a control of 171 +/‐ 2 ms by 39 +/‐ 2, 58 +/‐ 3, and 72 +/‐ 6 ms, respectively. Whole‐cell patch‐clamp experiments indicated that thiopental inhibited IK and IKl. Conclusions: Intravenous anesthetics caused markedly different effects on ventricular repolarization. Thiopental, unlike propofol and ketamine, potentiated the effects of erythromycin on ventricular repolarization by inhibiting IK and IKl.

Decreased Myocardial Contractility in Papillary Muscles from Atherosclerotic Rabbits

To determine the effect atherosclerosis has on myocardial contractility, we studied the contractile properties of right ventricular papillary muscles from 34 atherosclerotic and 17 control rabbits. We produced atherosclerosis by feeding for 2 to 8 months a diet of 5% lard, 5% peanut oil, 0.5% cholesterol, and 89.5% rabbit pellets. The controls received only rabbit pellets during the same time interval. Contracting isometrically 12 times per minute at 25°C, muscles from the atherosclerotic rabbits developed tension at a lower ma-rimum rate (max dT/dt), had a longer latency, and required longer to develop tension at the maximum rate and to develop peak tension. In isotonic contractions, they shortened with lower mmiimim velocities and required longer to accelerate to muTimiim velocity and to shorten maximally. We found no evidence that developed tension or distance shortened differed between the two groups of muscles. Raising the contraction frequency to 24 contractions ner minute brought performance of the two groups of muscles closer in both types of contraction. Norepinephrine (1.5 x 10-6M) nearly abolished differences between performance of the two groups. The loss of contractility correlates poorly with coronary and aortic atherosclerosis. It occurred early in the feeding of the atherogenic diet. We think it was due to a lipid-induced defect in the cardiac cells handling of calcium. Circ Res 45: 338-346, 1979

Interaction of Amphiphilic Molecules with Biological Membranes

The nonspecific interactions of propranolol, timolol, and ethanol with model and sarcoplasmic reticulum membranes were determined utilizing radioisotopic association, differential scanning calorimetry, and neutron diffraction. Differential scanning calorimetry performed on mixtures of these amphiphilic compounds and model membrane bilayers composed of dimyristoyllecithin showed that propranolol was approximately 25 times more lipid-soluble than timolol and at least 100 times more lipid-soluble than ethanol. Neutron diffraction showed that the solvation of propranolol was within the fatty acyl chain region of the lipid bilayer. This solvation correlated with the effect of propranolol to inhibit ATP-dependent calcium transport in isolated rabbit skeletal muscle sarcoplasmic reticulum, a membrane that lacks β-adrenergic receptors. In contrast, the major site of interaction of ethanol was within the aqueous compartment hydrating the sarcoplasmic reticulum membrane. A model for nonspecific drug interaction with the sarcoplasmic reticulum membrane based on the site of interaction of these amphiphiles and their relative potencies to inhibit calcium transport by these membranes is proposed. In principle, this model could be extended to specific drug interactions with membranes.

A rupture of both atrioventricular valves after blunt chest trauma: the usefulness of transesophageal echocardiography for a life-saving diagnosis.

Survival after the rupture of the both mitral and tricuspid valves in blunt thoracic trauma is uncommon and requires prompt diagnosis and treatment. We present a case in which transesophageal echocardiography performed in the operating room by the anesthesiologist identified the etiology of hemodynamic instability and facilitated successful emergency replacement of both valves.