No abstract

I The tension developed in the guinea-pig cremaster was recorded during spontaneous activity and electrical stimulation. Spontaneous rhythmic contraction was observed in many preparations, particularly in the tip of the cremaster. These contractions were very slow, lasting about 20 s and occurring at about 2 min intervals, but different preparations varied greatly. Twitches produced by electrical stimulation were similar to those in other skeletal muscles, being reduced by (+)-tubocurarine and abolished by tetrodotoxin. 2 A slow contraction could be initiated by electrical stimulation using a pulse longer than 10 ms in spontaneously active preparations and in some quiescent preparations. Spontaneous and evoked slow contractions were not suppressed by tetrodotoxin, but were selectively abolished by verapamil. Histamine increased the basal tension and generated spontaneous contractions in quiescent preparations. Hypertonic solutions also had excitatory effects. 3 Contractions produced by acetylcholine and carbachol were blocked by atropine. Those produced by adrenaline and noradrenaline were stronger than those due to histamine, acetylcholine and carbachol and were abolished by an ax-adrenoceptor blocking agent, phentolamine. In the preparations in which the slow contraction was not observed, histamine, acetylcholine or adrenaline had very little effect. 4 It is suggested that the cremaster muscle consists of striated muscle together with some smooth muscle having properties similar to that in the vas deferens.

SUMMARY1. Electrical responses of the smooth muscle cells to ATP were recorded in the longitudinal muscle of mouse myometrium, using intracellular micro-electrodes.2. ATP (> 10-7 M) dose-dependently produced a biphasic change in the membrane potential, an initial hyperpolarization (20-30 see) and then a depolarization. This effect of ATP was observed in all stages of gestation. The initial hyperpolarization was more quickly desensitized than the depolarization.3. Application of ATP for a short period (10 see) produced only the initial hyperpolarization; the amplitude was dose-dependently increased.4. During the ATP-induced hyperpolarization and the depolarization, generation of spike potentials was suppressed and enhanced, respectively. Strong outward current restored the spike generation during hyperpolarization.5. During the ATP-induced hyperpolarization, the membrane resistance was decreased. The amplitude of the hyperpolarization was increased in low [K]o solution and decreased in high [K]o solutions.6. Pre-treatment with TEA (1 mM), procaine (1 mM), 4-aminopyridine (0 5 mM) or apamin (2 x 10-7 M) did not, but TEA (5-10 mM) did suppress the ATP-induced hyperpolarization. Involvement of endogenous catecholamines, cyclic AMP, prostaglandins or acetylcholine in the ATP responses was ruled out.7. During the ATP-induced depolarization, the membrane resistance was reduced. In low [Na]0 solutions, the muscle membrane was depolarized and the amplitude of ATP-induced depolarization was reduced. In sodium-free solution, ATP produced only the initial hyperpolarization.8. It was concluded that the electrical responses ofthe smooth muscle cells of mouse myometrium to ATP consist of two components: an initial hyperpolarization with increase in the potassium conductance and a depolarization with increase in the sodium conductance.

In previous works it has been shown that the striated fibers of the cremaster muscle undergo a calcium-dependent healing-over reaction after transection and that the fibers of the diaphragm under the same conditions do not recover. In the present work striated fibers of the cremaster and diaphragm are studied, using electrophysiological techniques, light and electron microscopy, 15, 30, 45 and 6.0 min after transection in an attempt to clarify the process leading to the recovery of the fibers of the cremaster muscle. The recording of membrane potentials at different times after the lesion in the immediate vicinity of the cut end demonstrates that the new diffusion barrier is formed at the damaged surface. Light microscopy of fibers of cremaster transected in vitro indicates the existence of a rapid process preventing the outflow of particulate constituents of the cytoplasm 1 min after the lesion. Electron microscopy shows that this hindrance is due to a compact disposition of filaments derived from altered myofibrils near the cut end. This filamentary plug does not exist in the diaphragm. Cell membrane closing is a slow phenomenon which is completed between 30 and 60 min after the lesion in different fibers. No reconstitution of the cell membrane was found in the fibers of the diaphragm. Rapid and slow responses are interpreted as particular cases of the surface precipitation reaction known in several cell types for more than 40 years.

We investigated changes in membrane potential after small