Existence of a sodium‐induced calcium release mechanism of frog skeletal muscle fibres.

Abstract

SUMMARY1. The electrical and the mechanical activity of isolated frog muscle fibres have been simultaneously recorded in a physiological solution which allows the development of a large tubular sodium current.2. Under such experimental conditions, fibres develop long-lasting action potentials and strong mechanical responses.3. In voltage-clamp experiments a slow inward current is revealed for depolarizations higher than + 20 mV from the resting potential. This current increases until + 40 to + 50 mV and then decreases to reverse near + 90 mV. The amplitude of the mechanical response increases with the potential to reach an optimum value between + 40 and + 50 mV and then decreases to stabilize when the depolarization is near + 90 mV.4. In the presence of picrotoxin the slow inward current is reversibly inhibited and the tension-depolarization curve has an S-shape as found in normal physiological conditions. 5. The dependence of a part of the contraction upon the slow inward current is reinforced by the fact that in a 50 % sodium solution the amplitude of the current and that of the contraction are reduced in the same proportion. 6. Detubulated fibres failed to generate such a sodium inward current. 7. When sodium ions are replaced by lithium ions a slow inward lithium current develops but it does not induce a mechanical response.8. Tetracaine reversibly inhibits the current-dependent component of the contraction without affecting the potential-dependent one.9. It is concluded that the contraction recorded in the present experimental conditions is the sum of two components: one is potential-dependent and the other depends on a sodium-induced calcium release mechanism.

Selectivity of calcium channels in rat uterine smooth muscle: interactions between sodium, calcium and barium ions.

“…The action potentials are apparently mediated by voltage-dependent Ca channels since they vanish when external Na is removed or when Ca-channel blockers are added. Related findings were obtained on snail neurones (Kostyuk, Mironov & Shuba, 1983) and on muscle preparations (smooth muscle: Biilbring & Tomita, 1970; Prosser, Kreulen, Weigel & Yau, 1977; cardiac muscle: Garnier, Rougier, Gargouil & Coraboeuf, 1969;Miller, 1979; skeletal muscle: Potreau & Raymond, 1982; Almers, McCleskey & Palade, 1984). Uterine Ca channels are also permeable to divalent cations such as Ba and Sr (Jmari, Mironneau & Mironneau, 1986).…”

Maintained contractions of rat uterine smooth muscle incubated in a Ca2+‐free solution

“…Electrical activity was recorded with both conventional microelectrodes filled with 3 M KCI (resistance 40-50 MQ) and the double sucrose gap method (Mironneau, 1973 (Vassort & Rougier, 1972) and discussed in detail (Potreau & Raymond, 1983 (Lalanne et al, 1984). For longer applications of acetylcholine (2 min or more), the transient contraction was followed by a maintained response which lasted as long as the preparation was exposed to the agonist (Figure la (Figure 2).…”

Single low‐voltage‐activated calcium channels in chick and rat sensory neurones.

“…channel requires an only slightly higher [Ca2+]0 than that reported for the h.v.a. channel of different neurones (Kostyuk, Mironov & Shuba, 1983), neoplastic B lymphocyte (Fukushima & Hagiwara, 1985) and muscle fibres ; Hess & Tsien, 1984; see also Potreau & Raymond, 1982).…”