Platelets contained in concentrates prepared by intermittent flow centrifugation utilizing 5.0 g total ionized citrate, function normally as assessed by tests for adhesion, spreading, and ADP and collagen-induced aggregation. The ability of platelets to adhere and to aggregate following incubation with ADP is significantly reduced, in samples taken immediately after the collection procedure. Total platelet collection and platelet collection efficiency, is not compromised by use of the above citrate concentration.

Anticoagulants↗

PubMed1977

A study of the ion selectivity and the kinetic properties of the calcium dependent slow inward current in mammalian cardiac muscle.

1. A voltage-clamp method combining a single surcose gap and two intracellular micro-electrodes was used to measure membrane currents in ventricullar myocardial fibres. 2. The adequacy of the voltage-clamp method is demonstrated by comparing the total current, It, across the gap with the voltage difference, delta V, between the two intracellular micro-electrodes, i.e. another independent way of measuring membrane currents. With both current measurements the slow inward current, Is, shows the same voltage- and time-dependences. 3. The sensitivity of the slow inward current to variation in external Ca and Na concentrations was investigated systematically. The reversal potential of the slow inward current was sensitive to variation of both ion species. 4. From the reversal potential measurements relative permeabilities of the conductance channels of the slow inward current were estimated as PCa/PNa approximately 1/0-01 and PCa/PK approximately 1/0-01 by means of the constant field equation. 5. The activation and inactivation kinetics of the slow inward current were explored in detail and related to the plateau of the action potential.

Action Potentials↗

PubMed1977

The regulation of the calcium conductance of cardiac muscle by adrenaline.

1. The effect of adrenaline on the Ca-dependent slow inward current, Is, of mammalian cardiac muscle has been investigated by the voltage-clamp method. The mechanism of the increase in the conductance, gs, was analysed on the basis of a kinetic scheme (Hodgkin & Huxley, 1952) applicable to this system. 2. The rate constants alphad and betad, of activation of gs were not influenced by adrenaline, although the limiting conductance, gs, was greatly increased. 3. Reduction of [Ca]o from 1-8 to 0-2 mM decreased the amplitude of inward tail currents when gs was fully activated; however, the relative decrease of the current amplitude was the same with and without adrenaline. The reversal potential, ER, of Is was not changed by the drug. This indicates that the catecholamine has no influence on the selectivity of these conductance channels. 4. An increase in the number of functional conductance channels by adrenaline is discussed as a possible mechanism for the increase in Gs.

Animals↗

PubMed1977

Reconstruction of the action potential of ventricular myocardial fibres.

1. A mathematical model of membrane action potentials of mammalian ventricular myocardial fibres is described. The reconstruction model is based as closely as possible on ionic currents which have been measured by the voltage-clamp method.2. Four individual components of ionic current were formulated mathematically in terms of Hodgkin-Huxley type equations. The model incorporates two voltage- and time-dependent inward currents, the excitatory inward sodium current, i(Na), and a secondary or slow inward current, i(s), primarily carried by calcium ions. A time-independent outward potassium current, i(K1), exhibiting inward-going rectification, and a voltage- and time-dependent outward current, i(x1), primarily carried by potassium ions, are further elements of the model.3. The i(Na) is primarily responsible for the rapid upstroke of the action potential, while the other current components determine the configuration of the plateau of the action potential and the re-polarization phase. The relative importance of inactivation of i(s) and of activation of i(x1) for termination of the plateau is evaluated by the model.4. Experimental phenomena like slow recovery of the sodium system from inactivation, frequency dependence of the action potential duration, all-or-nothing re-polarization, membrane oscillations are adequately described by the model.5. Possible inadequacies and shortcomings of the model are discussed.

Action Potentials↗

PubMed1977