Responses to stretch and the effect of pull on propagation in non-striated muscles of Golfingia (Phascolosoma) and mustelus.

In the short-fibered non-striated probascis retractor of phascolosoma (Golfingia gouldii) , 3 conduction is entirely by intrinsic nerve fibers. Evidence for nerve conduction is: velocity of propagation (1.3 and 0.3 m/second for fast and slow responses, respectively), abundance of nerve fibers, block by nerve-blocking drugs, failure of propagation after nerve degeneration, and detection of nerve impulses ahead of muscle responses (Prosser and Melton, '54). Conduction in other non-striated postural muscles of invertebrates appears also to be by nerves. In vertebrate visceral smooth muscle, in contrast, conduction is from fiber to fiber independently of nerves and is very slow (few centimeters per second) (Bozler, '48, Prosser and Sperelakis, '56). In the circular intestinal muscle of the cat, conduction can pass a region clamped to prevent mechanical pull, it can occur under such tension that shortening is prevented, and mechanical and electrical responses can be partly dissociated by drugs (Sperelakis and Prosser, '59); hence mechanical pull appears unnecessary for muscle activation. However, some smooth muscles are stimulated by stretch, even in the absence of nerves and myenteric reflexes (e.g., chick amnion, Evans and Schild, '56) and many smooth muscles show increased excitability when they are extended (e.g., taenia coli of guinea pig, Bulbring, '54). Is conduction in visceral smooth muscle of lower vertebrates and invertebrates independent of nerves? What is the relation between mechanical pull and conduction in muscles which are stimulated by stretch? MATERIALS AND METHODS