The transmission of excitation from the membrane to actomyosin

The ineffectiveness of the ‘window field’ in the initiation of muscle contraction

“…They recognize that, in order to maintain this theory, contraction must be shown to occur along the whole length of a muscle fibre when it is placed in a field of sufficient intensity, even in the absence of an action potential. Bay et al (1953) claim that this occurred in an experiment in which the muscle was treated with novocaine and then subjected to a longitudinal field.…”

Is muscle contraction initiated by internal current flow?

“…Recently Csapo (1957) and Csapo & Suzuki (1958) have attempted to revive the now obsolete 'window field' theory of Bay et al (1953) by putting forward the hypothesis that it is the combined action of depolarization and internal current flow which causes contraction in a muscle fibre. The modified 'window field' theory is said to be consistent with the view that the fibrils within the fibre are stimulated to contract by the longitudinal current flowing through them, e.g.…”

“…This concept has also been advocated at some length in a recent review (Gelfan, 1958). What Csapo & Suzuki (1958) appear to have done is to modify the 'window field' theory of Bay et al (1953) so as to make it consistent with some of the evidence which was brought forward against it in its original form. However, their supporting evidence differs in essential aspects from the results of all the other investigations in the same field (Katz & Lou, 1947;Sten-Knudsen, 1954;Csapo & Wilkie, 1956;Hodgkin & Horowicz, 1956).…”

“…The original 'window field' theory proposed by Bay et al (1953) was opposed on the grounds that, in the absence of propagation, internal current flow causes contraction only at points on the fibre where the membrane is being depolarized and not along its whole length (Kuffler, 1946;Sten-Knudsen, 1954;Huxley & Taylor, 1955, 1958Watanabe & Ayabe, 1956). The modified 'window field' theory of Csapo & Suzuki (1958) is consistent with this set of observations, although it is difficult to reconcile this theory with the observation that a longitudinal d.c. field, when applied to a muscle in moderate contracture, causes relaxation in part of the anodic region, while contraction is enhanced only in the cathodic region (Kuffler, 1946;Sten-Knudsen, 1954).…”

“…Csapo & Suzuki have put forward the theory that it is the combined action of depolarization and internal current flow which elicits contraction. This is a modification of the now discarded 'window field' theory of Bay et al (1953). Membrane depolarization is considered a necessary 'priming' step which by itself is ineffective in setting off contraction.…”