Andrew Huxley

How molecular motors work in muscle

Much of Howards Review Article concerns the results of experiments with single myosin molecules and actin filaments. It was a huge surprise when reports of such experiments first appeared (see, for example, ref. 2), and much is being learnt from them that cannot be deduced from experiments on whole muscle fibres, whether intact or after removal of the membrane. But single-molecule experiments do not yet approach the time resolution or the freedom from brownian noise that are easily attainable on larger assemblies of myosin and actin filaments, and their interpretation is subject to many uncertainties — due, for instance, to compliance in the actin filaments and in their attachments to beads or other force-measuring components, and the attachment of myosin molecules or fragments to the base. No doubt the time course of the working stroke of a single myosin head will one day be recorded, but until that is achieved the results of experiments on whole fibres and myofibrils deserve more careful attention than has been given to them by Howard.

Muscle: Support for the lever arm

Length changes in muscle result from the relative sliding of filaments composed of myosin and actin; the heads of the myosin molecules attach to the actin, exert force and then detach. Several papers provide further evidence for the view that the myosin head acts as a lever arm in this process, rather than tilting as a whole, and for the extent of lever-arm movement.

Biological actions of calcium.

This meeting is being held to celebrate a great advance that was made forty years ago by Professor Setsuro Ebashi. This was the discovery of the substance “troponin”,1 a component of the thin filaments of striated muscle of vertebrates. A few years earlier,2 Ebashi had given direct evidence that calcium ions, at a concentration of a few micromolar, cause contraction of actomyosin preparations. This was a remarkable achievement, since at that time calcium chelators were not available, and the level of calcium impurities had to be kept down by extreme care in preparation of his solutions. This observation was made while Ebashi was spending a year in the laboratory of Fritz Lipmann in New York. On his way back to Japan in 1960, he passed through Britain and took the opportunity of coming to Cambridge to visit Alan Hodgkin and myself. He told us of his observations, and also said that Lipmann had been unwilling to accept that anything as simple as a calcium ion could perform such an important and specific function, and that this had delayed Ebashi’s publication of his results. Later, Ebashi told me that he had been much encouraged by my enthusiastic response to what he told us.

The Pali Buddhist Approach to Human Cloning

Pali Buddhism would approach this ethical issue from three directions: n n1. n nquestioning the motives of the cloners n n n n nHuman n ncloning involves intentional human action: do we classify this action as ‘skilful’ or ‘unskilful’ (in Pali, kusala/akusala kamma; in English, good or bad karma)? n n n n n2. n nprotecting the interests of the cloned n n n n nBuddhists n nare committed to treat all sentient beings with metta (loving-kindness). From this derives an analysis that overlaps with the European rights / interests / expectations approach.1 Will a cloned human, qua cloned, get less metta than a standard-issue human? n n n n n3. n nIs the cloning process itself ethically flawed? n n n n nWould n nhuman cloning weaken institutions — such as the family — on which human flourishing depends? Or would it interfere with natural processes — such as karma — on which the flourishing of all sentient beings depends?

BA address: Huxley responds

Sir Andrew Huxley, Royal Society Research Professor in the Department of Physiology at University College London, responds to Natures editorial on the presidential address he delivered to the recent British Association meeting